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      Leptospirosis: A Silent Epidemic Disease

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          Abstract

          This special issue of International Journal of Environmental Research and Public Health is dedicated to leptospirosis, an endemic zoonotic disease that is a cause of many acute undifferentiated fevers, especially in tropical countries [1,2]. While it can be debated whether leptospirosis is an emerging disease, it is evident that it is becoming an emerging public health problem. It is recognized as a disease of epidemic potential that has a significant health impact in many parts of the world. Leptospirosis is an excellent example of “One Health”, where the relationship between humans, animals and ecosystems can be used to improve our understanding of this disease and to enhance control strategies [3]. The bacteria Leptospira interrogans is pathogenic to humans and animals. It affects a wide variety of animal species, both wild and domestic, which serve as sources of infection for humans [4]. Exposure through water and soil contaminated by the urine of infected animals is the most common route of transmission to people and domestic animals [4]. The burden of leptospirosis is estimated to be 500,000 persons worldwide per year, although new estimations are being developed by an expert consultation group led by the World Health Organization (WHO) [5]. In addition, the number of reported cases associated with natural disasters and flooding have increased with the most notable outbreaks occurring in: Nicaragua (1995), Peru and Ecuador (1998), Orissa (1999), Malaysia (2000), Jakarta (2002), Mumbai (2000 and 2005), and The Philippines (2009) [6,7,8,9,10,11,12]. Reviewing the HealthMap database that utilizes different online sources for real-time surveillance of emerging public health threats, there were 787 global alerts for leptospirosis between 2007 and 2013 [13]. More than half of these leptospirosis alerts (63%) occurred in the Americas Region, particularly in Brazil (142 alerts), Nicaragua (45) and Argentina (43) [13]. About ten million people are affected by natural disasters in the Region of the Americas annually, with the majority of them being storms (41%) and floods (35%) [14,15]. However, only half of the countries in this region have reported leptospirosis case surveillance data, which suggests that not all countries have recognized leptospirosis as an important public health threat [16]. The region with the second highest percentage of alerts is the Western Pacific (15%), followed by South-East Asia (14%) and Europe (8%) [13]. The African (1%) and the Eastern Mediterranean Regions (0.5%) do not present many leptospirosis alerts, possibly due to their diagnostic capabilities [13]. Leptospirosis cases have been reported in a variety of settings, from large urban centers after floods to remote rural areas with limited access to clean drinking water and sanitation [17,18,19,20]. While it affects mostly vulnerable populations and is often considered a disease of poverty in middle and low income countries; it is also considered an occupational disease affecting rice workers, animal handlers (farmers, veterinarians, butchers), sewer workers, gold mining workers, among others in low, middle and high income countries alike [4,21,22,23]. In recent years, leptospirosis has gained increased attention as it relates to recreational activities among the wildlife and army expeditions [8,24]. The impact on humans may be devastating since the disease can result in hospitalization and time lost from work [25]. In addition, leptospirosis outbreaks pose a burden on health systems and can cause significant economic and social disruption. Leptospirosis is typically underdiagnosed and underreported. With symptoms ranging from a mild flu-like illness to a more severe and sometimes fatal disease (mortality rate greater than 10%), differentiating leptospirosis from diseases with similar non-specific symptoms such as dengue, malaria and influenza becomes arduous [1,26,27]. Furthermore, laboratory confirmation is difficult as diagnostic tests are expensive and require specific training and equipment, often only found at reference labs. Despite these difficulties, leptospirosis remains one of the top ten infectious hazards reported globally in the Event Management System (EMS), the event system that supports the International Health Regulations since its revised version implemented in 2007 [28,29]. In the Americas, leptospirosis events were in the top third, and came only after dengue and influenza as top infectious hazards in the EMS. Animal leptospirosis can cause a significant economic impact to local farmers and national economies since it is related to reduced milk production and livestock abortions [30]. Local studies in Central America already indicate the importance of this disease in animals, given that leptospirosis prevalence was found in bovine (31–83%), equine (18–76%), porcine (17–75%) and canine (27–65%), among others animals [31]. Because only a few studies can be found in the literature about the impact of leptospirosis on livestock production, both in small farms and in extensive livestock raising practices, there is an urgent need to have additional studies evaluating its impact and the cost-effective actions required in order to reduce the spread of this disease from animals to humans. Further, the role that the environment has on leptospirosis outbreaks is not well understood. Recent evidence suggests that climate change may be correlated to the increased number of outbreaks. In addition, research indicates that heavy rains or floods may be drivers for this disease [18,32,33,34,35]. Another possible driver is type of alkaline and neutral soil, which may facilitate longer survival of the bacteria, especially in volcano origin soils [18,30]. Certain ecological conditions may propagate the circulation of peri-domestic rodents and contribute to intensive agriculture production [36]. Also, higher risk of infection has been associated with vulnerable populations living in dense urban or peri-urban areas without waste collection and with inadequate sanitation [33,37]. An increased level of understanding regarding the risk factors could provide information to support countries’ decision makers in identifying risk areas for priority interventions. Leptospirosis remains as a neglected disease that suffers from unawareness, despite its increasing number of cases and outbreaks globally [28]. However, the impact this disease has on various sectors, on numerous risk groups, in many countries, and in a variety of settings demonstrates the importance of addressing leptospirosis with a holistic approach in a global perspective. This special issue on leptospirosis in the animal-human-ecosystem interface highlights a range of topics, from the complexities surrounding disease transmission between animals, rodents and humans to the need for developing economical preventive and control methods. It demonstrates the importance of developing interdisciplinary, multi-sectorial groups, as the Global Leptospirosis Environmental Action Network (GLEAN), a network which translates research into operational tools to support communities and countries affected by leptospirosis [38]. It brings to light country specific initiatives and research focusing on the socioeconomic factors related to leptospirosis outbreaks and also addresses the impact leptospirosis has on animals. It points out the need for further research on laboratory diagnosis and vaccines for both humans and animals. It is evident that an integrated vision within the animal-human-ecosystem interface is necessary in order to orient knowledge about the prediction, detection, prevention and response to outbreaks of leptospirosis. The complex nature of the transmission of leptospirosis and the gap of practical tools to operate at the local level by both human and animal health authorities is a major challenge and it remains for the scientific community to address. We hope this issue will bring to light the many components surrounding leptospirosis as well as promote the need for further research, collaboration, and innovative ideas necessary reduce its global impact.

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          Etiology of Severe Non-malaria Febrile Illness in Northern Tanzania: A Prospective Cohort Study

          Introduction Fever without a localized cause is one of the most common presenting complaints among persons seeking healthcare in many low- and middle-income countries [1], [2]. However, unlike the syndromes of pneumonia and diarrhea that feature in global disease burden estimates and have well coordinated programs integrating efforts across the range of responsible pathogens to avert morbidity and mortality, there has been a lack of a coordinated approach for febrile illness. While illness and death due to some specific infections causing fever, such as malaria [3] and increasingly bacterial sepsis are well quantified [4]–[6], others such as a range of zoonoses and viral infections are uncounted and consequently may be underappreciated. The various etiologies of febrile illnesses are difficult to distinguish from one another clinically [7], [8]. As clinical laboratory services are often limited in areas where febrile conditions are particularly common [9], [10], clinicians may have few diagnostic tools to establish an etiologic diagnosis. Therefore, clinical management is often driven by syndrome-based guidelines employing empiric treatment [11]–[13]. In the absence of systematically collected data on fever etiology, considerable mismatch between clinical diagnosis, clinical management, and actual etiology may occur resulting in poor patient outcomes [14]. It is increasingly recognized that malaria is over-diagnosed in many areas [14], [15]. To address this problem, the World Health Organization (WHO) malaria treatment guidelines moved away from clinical diagnosis of malaria to treatment based on the results of a malaria diagnostic test such as a blood smear or a malaria rapid diagnostic test. With more widespread availability of diagnostic tests to exclude malaria and apparent declines in malaria worldwide [3], clinicians in resource-limited areas are faced with a growing proportion of febrile patients who do not have malaria and few tools to guide subsequent management. We sought to describe comprehensively the causes of febrile illness in northern Tanzania among patients sufficiently ill to require hospitalization. Febrile patients admitted to two hospitals were evaluated for a wide range of infectious etiologies using conventional standard diagnostic techniques. Methods Ethics statement This study was approved by the Kilimanjaro Christian Medical Centre (KCMC) Research Ethics Committee, the Tanzania National Institutes for Medical Research National Research Ethics Coordinating Committee, and Institutional Review Boards of Duke University Medical Center and the CDC. All minors had written informed consent given from a parent or guardian and all adult participants provided their own written informed consent. Setting Moshi (population, >144 000) is the administrative center of the Kilimanjaro Region (population, >1.4 million) in northern Tanzania and is situated at an elevation of 890 m above mean sea level. The climate is characterized by a long rainy period (March–May) and a short rainy period (October–December) [16]. Malaria transmission intensity is low [17]. KCMC is a consultant referral hospital with 458 inpatient beds serving several regions in northern Tanzania, and Mawenzi Regional Hospital (MRH), with 300 beds, is the Kilimanjaro Regional hospital. Together KCMC and MRH serve as the main providers of hospital care in the Moshi area. In 2008, KCMC admitted 22,099 patients and MRH admitted 21,763 patients. Study design A study team that was independent of the hospital clinical team identified participants among infants and children admitted to KCMC from 17 September 2007 through 25 August 2008, and among adolescents and adult admitted to KCMC and MRH in Moshi, Tanzania, from 17 September 2007 through 31 August 2008. The methods of these studies have been described in detail elsewhere [7], [8]. In brief, all admitted patients were screened for eligibility by study team members as soon as possible after admission and no later than 24 hours after admission. Infants and children aged from ≥2 months to <13 years, with a history of fever in the past 48 h or an axillary temperature ≥37.5°C or a rectal temperature of ≥38.0°C, and adolescents and adults aged ≥13 years and with oral temperatures of ≥38.0°C were invited to participate in the study. Patients admitted with known malignancy, renal failure, hepatic failure, bone marrow aplasia, trauma or surgery were excluded. A standardized clinical history and physical examination were performed on consenting patients by a trained clinical officer who was a member of the study team and who worked in parallel with the hospital admitting team. Provisional diagnoses by the hospital clinical team made independently of the study team were recorded and coded using the International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) codes. Following cleansing of the skin with isopropyl alcohol and povidone iodine, blood was drawn from adults and adolescents for aerobic blood culture (5 mL) and for mycobacterial blood culture (5 mL) and from pediatric patients for a single aerobic blood culture (4 ml). In addition, blood was drawn for complete blood count, examination for blood parasites, and HIV antibody testing. Acute serum, plasma, and whole blood were archived on all participants. For patients found to be HIV seropositive, CD4-positive T lymphocyte count (CD4 cell count) and serum cryptococcal antigen level were also measured. HIV-seronegative patients were screened for the presence of acute HIV infection by polymerase chain reaction (PCR) for HIV-1 RNA. Urine was collected as soon as possible after admission for detection of urine antimicrobial activity and for antigen detection. A discharge form was completed at the time of discharge from the hospital that captured whether the patient died in hospital, the in-hospital management, and the discharge diagnoses coded using ICD-10 codes. The results of study investigations done in Moshi were provided immediately to the hospital clinical team to inform patient management. The results of investigations done at reference laboratories were provided to the hospital clinical team as they became available. The hospital clinical team was responsible for all aspects of patient management, following clinical judgment and use of locally adapted and developed treatment guidelines. All participants were asked to return to a study clinic 4–6 weeks after enrollment to provide a convalescent serum sample. To promote high levels of follow up, the study team provided a follow up appointment card prior to hospital discharge, made reminder telephone calls to participants during the week prior to the appointment, reimbursed travel expenses of returning participants, and when necessary a field worker made home visits. Laboratory evaluations Laboratory evaluations were selected to reflect a range of infectious diseases that might occur in northern Tanzania. Priority was given to laboratory evaluations for infectious diseases that might require specific management. Malaria Thick and thin blood films stained with Giemsa were examined for blood parasites by oil immersion microscopy. Parasite density was determined by standard methods [18]. Bacteria and fungal bloodstream infections Blood culture bottles were assessed for volume adequacy comparing the weight before and after inoculation with blood. Adequate volume was defined as the recommended volume ±20%. BacT/ALERT standard aerobic and mycobacterial bottles were loaded into the BacT/ALERT 3D Microbial Detection system (BioMérieux), where they were incubated for 5 and 42 days, respectively. Standard methods were used for identifying bloodstream isolates [7], [8]. Serum antigen testing Cryptococcal antigen level was measured using the Latex Cryptococcal Antigen Detection System assay (Immuno-Mycologics). Urine antigen testing Urine was tested for all participants for Legionella pneumophila serogroup 1 antigen using the Binax NOW Legionella urinary antigen test, and for adolescents and adults using the Sreptococcus pneumoniae using the Binax NOW S. pneumoniae antigen test (Binax). Urine was tested for Histoplasma capsulatum antigen using the MVista H. capsulatum quantitative antigen enzyme immunoassay (Miravista Diagnostics) [19], [20]. Leptospirosis Leptospirosis laboratory diagnosis was made using the standard microscopic agglutination test (MAT) performed at the CDC. Live leptospiral cell suspensions representing 20 serovars and 17 serogroups described elsewhere [21] were incubated with serially diluted serum specimens. Resulting agglutination titers were read using darkfield microscopy. The reported titer was the highest dilution of serum that agglutinated at least 50% of the cells for each serovar tested [22]. Confirmed leptospirosis was defined as a ≥4-fold rise in the agglutination titer between acute and convalescent serum samples [23]. Brucellosis Brucellosis serology was performed using the standard microagglutination test (MAT) performed at the CDC. Standardized Brucella abortus strain 1119-3 killed antigen (National Veterinary Services Laboratory, Ames, IA) was used for MAT at a 1∶25 working dilution described elsewhere [24]. Results were read on a Scienceware Plate Reader (Bel-Art Products, Wayne, NJ). Minor modifications were made to the CDC's standard MAT, including the use of U-bottom plates, incubation at 26°C, and discontinued use of staining techniques [25]. Confirmed brucellosis was defined as a ≥4-fold rise in the agglutination titer between acute and convalescent serum samples. Q fever Convalescent-phase serum samples were screened using C. burnetii immunoglobulin (Ig) G enzyme-linked immunosorbent assay (ELISA) against Phase II antigen (Inverness Medical Innovations). For samples that were either positive or equivocal by ELISA, paired serum samples were tested by indirect immunofluorescence antibody (IFA) IgG assay to C. burnetii (Nine Mile strain) Phase I and Phase II antigens. A fourfold or greater increase in IFA reciprocal titer to Phase II antigen defined acute Q fever [26]. Spotted fever group and typhus group rickettsioses Serum samples were tested for SFGR and TGR by IgG IFA to R. conorii (Moroccan strain) and to R. typhi (Wilmington strain), respectively. Among paired serum samples, a fourfold or greater increase in IFA titer to R. conorii and R. typhi defined acute SFGR and TGR infections, respectively [26]. Arboviruses RNA was extracted from serum samples using the QIAamp Viral RNA Mini kit (QIAGEN, Hilden, Germany). Reverse transcription was performed using Invitrogen Superscript III First Strand Synthesis System (Life Technologies, Carlsbad, CA). Real-time PCRs for flavivirus, DENV, and CHIKV were carried out with the LightCycler 480 SYBR Green I Master kit (Roche Diagnostics, Penzberg, Germany) in a total reaction volume of 20 µL containing 2 µL of cDNA using primers published elsewhere [27]–[29]. Confirmed acute CHIKV, DENV, and flavivirus infections were defined as a positive PCR result for CHIKV, DENV, and flavivirus viral RNA, respectively [30]. HIV HIV-1 antibody testing was done on whole blood using both the Capillus HIV-1/HIV-2 (Trinity Biotech) and Determine HIV-1/HIV-2 (Abbott Laboratories) rapid HIV antibody tests. The Capillus test was replaced with the SD Bioline HIV-1/HIV-2 test (version 3.0; Standard Diagnostics) on 4 March 2008 after a change in Tanzania Ministry of Health HIV testing guidelines. If rapid tests were discordant, the sample was tested using enzyme-linked immunosorbent assay (ELISA; Vironostika Uni-Form II plus O Ab; bioMe'rieux). If the ELISA was negative, no further testing was done. If the ELISA was positive, a Western blot (Genetic Systems HIV-1 Western blot kit; Bio-Rad) was done to confirm the result [31]. HIV-1 RNA PCR was done using the Abbott m2000 system RealTime HIV-1 assay (Abbott Laboratories) [32], [33]. Statistic analysis Data were entered using the Cardiff Teleform system (Cardiff Inc., Vista, Ca., USA) into an Access database (Microsoft Corp, Va., USA). When a diagnostic test was not applied to the whole cohort due lack of availability of an acute or convalescent sample, the proportion of confirmed cases in the tested group was extrapolated to the untested group by assuming that prevalence was the same in the tested group as in the untested group. Statistical analyses were performed with SAS version 9.1 software (SAS Inc, Cary, NC). Results Participant characteristics Figure 1 summarizes participant screening, enrollment, and diagnostic testing. Of 870 febrile admissions to two hospitals in northern Tanzania enrolled in the study 484 (55.6%) were female. Of participants, 467 (53.7%) were infants and children with a median (range) age of 2 years (2 months - 13 years); the remainder adolescents and adults with a median (range) age of 38 (14–96) years. Fifty seven (12.2%) infants and children were HIV-infected compared with 157 (39.0%) adolescents and adults. Among infants and children 34 (7.3%) of 464 with hospital outcome data died; 2 (5.9%) of those who died had invasive infections. Among adolescents and adults, 41 (10.3%) of 398 with hospital outcome data died; 11 (26.8%) of those who died had invasive infections. In hospital deaths could not be attributed to etiologies requiring serologic diagnosis due to the requirement for testing a convalescent serum sample. 10.1371/journal.pntd.0002324.g001 Figure 1 Study flow diagram. KCMC: Kilimanjaro Christian Medical Centre; MRH: Mawenzi Regional Hospital; MAT: microagglutination test; IFA: immunoflouresence assay; NAAT: nucleic acid amplification test. Proportions of febrile admissions attributed to specific etiologies Table 1 shows the number of patients with acute and convalescent samples available for testing for each etiologic agent or group of etiologic agents. Not all tests could be applied to all participants because of limited volumes of sample for some participants, and by the lack of availability of convalescent serum for participants who died before the follow up visit or who did not return. The number of confirmed cases in each group is also shown. The proportion of febrile admissions attributed to each etiology is calculated. A complete sample set was available for 243–467 (52.0–100.0%) infants and children and for 207–403 (51.4–100.0%) adolescents and adults. 10.1371/journal.pntd.0002324.t001 Table 1 Calculation of the proportion of hospitalized infants and children, and adolescents and adults, with specific etiologies of febrile illness, northern Tanzania, 2007–8. Etiology Infants and children Adults and adolescents All n confirmed cases n tested (%) n confirmed cases n tested (%) n confirmed cases n tested (%) Bloodstream infections Bacterial 16 467 (3.4) 69 403 (17.1) 85 870 (9.8) Mycobacterial 0 467 (0.0) 14 403 (3.5) 14 870 (1.6) Fungal 4 467 (0.9) 21 403 (5.2) 25 870 (2.9) Malaria 6 467 (1.3) 8 403 (2.0) 14 870 (1.6) Subtotal 26 467 (5.6) 112 403 (27.8) 138 870 (15.9) Bacterial zoonoses Brucellosis 5 246 (2.0) 11 207 (5.3) 16 453 (3.5) Leptospirosis 19 246 (7.7) 21 207 (10.1) 40 453 (8.8) Q fever 7 268 (2.6) 17 215 (7.9) 24 482 (5.0) Spotted fever group rickettsioses 18 243 (7.4) 18 207 (8.7) 36 450 (8.0) Typhus group rickettsioses 0 243 (0.0) 2 207 (1.0) 2 450 (0.4) Subtotal 49 243 (20.2) 69 207 (33.3) 118 450 (26.2) Arboviruses Chikungunya 34 332 (10.2) 21 368 (5.7) 55 700 (7.9) Flaviviruses 0 332 (0.0) 0 368 (0.0) 0 700 (0.0) Subtotal 34 332 (10.2) 21 368 (5.7) 55 700 (7.9) No diagnosis (64.0) (33.2) (50.1) Due to changing denominators for individual diagnostic tests, the proportion with no diagnosis is calculated as the proportion without a positive result from any test. Bloodstream infections are those diagnosed predominantly by blood culture, including organisms such as Salmonella enterica, Streptococcus pneumoniae, Cryptococcus neoformans, and Mycobacterium tuberculosis. Bacterial zoonoses, including brucellosis, leptospirosis, Q fever, and rickettsioses were diagnosed predominantly by serology, based on a 4-fold or greater rise in antibody titer between an acute and convalescent sample. Etiology of fever among infants and children Of 467 infants and children enrolled, malaria was the clinical diagnosis for 282 (60.4%), but was the actual cause of fever in 6 (1.3%). Bacterial and fungal bloodstream infections described in detail elsewhere [8] accounted for 16 (3.4%) and 4 (0.9%) febrile admissions, respectively, and were underrepresented on admission differential diagnoses. Bacterial zoonoses were identified among 49 (20.2%) of febrile admissions; 5 (2.0%) had brucellosis, 19 (7.7%) leptospirosis, 7 (2.6%) had Q fever, 18 (7.4%) had spotted fever group rickettsioses, and none had typhus group rickettsioses. In addition, 34 (10.2%) of participants had a confirmed acute arbovirus infection, all due to chikungunya (Table 1). No patient had a bacterial zoonoses or an arbovirus infection included in the admission differential diagnosis. Etiology of fever among adolescents and adults Of 403 adolescents and adults enrolled, malaria was the clinical diagnosis for 254 (63.0%), but was the actual cause of fever in 8 (2.0%). Bacterial, mycobacterial, and fungal bloodstream infections described in detail elsewhere [7] accounted for 69 (17.1%), 14 (3.5%), and 21 (5.2%) febrile admissions, respectively, and were underrepresented on admission differential diagnoses. Bacterial zoonoses were identified among 69 (33.3%) of febrile admissions; 11 (5.3%) had brucellosis, 21 (10.1%) leptospirosis, 17 (7.9%) had Q fever, 18 (8.7%) had spotted fever group rickettsioses, and 2 (1.0%) had typhus group rickettsioses. In addition, 21 (5.7%) of participants had a confirmed acute arbovirus infection, all due to chikungunya (Table 1). No patient had a bacterial zoonosis or an arbovirus infection included in the admission differential diagnosis. Etiology of fever overall Among all 870 participants, malaria was the clinical diagnosis for 528 (60.7%), but was the actual cause of fever in 14 (1.6%). By contrast, bacterial, mycobacterial, and fungal bloodstream infections accounted for 85 (9.8%), 14 (1.6%), and 25 (2.9%) febrile admissions, respectively, and were underrepresented on admission differential diagnoses. Bacterial zoonoses were identified among 118 (26.2%) of febrile admissions; 16 (13.6%) had brucellosis, 40 (33.9%) leptospirosis, 24 (20.3%) had Q fever, 36 (30.5%) had spotted fever group rickettsioses, and 2 (1.8%) had typhus group rickettsioses. In addition, 55 (7.9%) of participants had a confirmed acute arbovirus infection, all due to chikungunya (Table 1). No patient had a bacterial zoonoses or an arbovirus infection included in the admission differential diagnosis. The proportional etiology of febrile illness among study participants after extrapolating to the untested group is summarized in Figure 2. 10.1371/journal.pntd.0002324.g002 Figure 2 Laboratory confirmed causes of febrile illness among infants and children (panel A) and adolescents and adults (panel B) hospitalized in northern Tanzania, 2007–8*. *In instances that diagnostic test results were not available for all participants, the proportion positive from Table 1 was applied to the whole study population. Pie graphs do not account for concurrent infections. A complete listing of specific bacterial, mycobacterial, and fungal bloodstream infections is available elsewhere [7], [8]. Discussion We demonstrate among hospitalized febrile patients in northern Tanzania that malaria is uncommon and over-diagnosed, while invasive bacterial, mycobacterial, and fungal infections are underappreciated. At the same time, the bacterial zoonoses leptospirosis, Q fever, and spotted fever rickettsioses, and to a lesser extent brucellosis, and the arbovirus infection chikungunya are common yet unrecognized causes of fever. Our findings point to important mismatches between clinical diagnosis and management with actual diagnoses that have major implications for patient care, disease control and prevention, and for judicious use of antimalarial medications. While the problem of malaria over-diagnosis has been appreciated for some time [14], [15], studies that comprehensively describe the causes of severe non-malaria fever requiring hospital admission beyond bloodstream infections have been lacking. The over-diagnosis of malaria results in inappropriate use of antimalarial medications and may be associated with higher case fatality rates among patients treated for malaria who do not have the infection [14], [15], [34]. While the underlying causes of the over-diagnosis of malaria are complex [35], the lack of epidemiologic information about the importance of alternative infections and guidance on their management is likely to play a role. Our findings confirm the potential benefits of making reliable malaria diagnostic tests available at healthcare facilities and using the results as the basis for prescription of antimalarial medications [36]. When adopted, such an approach to malaria treatment would support the judicious use of antimalarials and would define the population of patients with nonmalaria fever. We found that the bacterial zoonoses, leptospirosis, Q fever, and spotted fever group rickettsioses, and to a lesser extent brucellosis, are major causes of febrile illness among patients sufficiently unwell to require hospitalization. That a group of neglected bacterial zoonoses are of major clinical and public health importance in sub-Saharan Africa is a new and paradigm-changing finding. For clinical practice, with the exception of leptospirosis that may be effectively treated with commonly prescribed antibacterials, patients with brucellosis, Q fever, and the rickettsioses are likely to leave hospital without specific treatment. In northern Tanzania where many rely on livestock for their health and economic wellbeing, Leptospira, Brucella, and Coxiella spp. also indirectly affect human health through their impact on animal fertility, growth, and survival. The control and prevention of the neglected bacterial zoonoses is likely to involve interventions that require the collaboration of human health experts with the animal and environmental health disciplines, an approach that is underdeveloped in many parts of the world. Clinical guidelines for management of febrile patients in low resource areas focus on the identification and treatment of malaria and bacterial sepsis [11]–[13]. Our findings suggest that there is a need to identify and incorporate guidance on when to use a tetracycline for treatment of Q fever or rickettsial infection and when to consider treatment for brucellosis. We have previously demonstrated that features of the clinical history and physical examination do not perform well for identifying fever etiology [7], [8], [21], [26], [30]. Therefore, improvements to treatment algorithms for febrile patients are likely to require the development and incorporation of reliable diagnostic tests that provide timely diagnostic information to clinicians [37]. Unfortunately, many rapid diagnostic tests for infections related to fever management other than malaria and HIV suffer from poor performance characteristics [38], [39]. Lack of coordination among groups working on the various etiologies of febrile illness in low-resource areas has meant that sentinel studies that could provide much more comprehensive information on a wide range of responsible organisms instead have focused on only one or a small handful of etiologies. For example, a clinical trial evaluating the impact of pneumococcal conjugate vaccine on rates of Streptococcus pneumoniae bacteremia in a community has the potential to identify and report all bloodstream infections. Similarly, a study designed to estimate the incidence of typhoid fever to inform vaccine policy could collect acute serum along with the blood culture and, with subsequent collection of convalescent serum, would have the ability to estimate the incidence of leptospirosis and a range of other etiologic agents using conventional serologic methods [40]. However, resources for research have tended to be targeted to specific pathogens and researchers have struggled to leverage additional resources to address a broader range of organisms. Sentinel site studies seeking to understand the infectious causes of febrile illness in low-resource settings have utilized blood culture to highlight the importance of invasive bacterial and fungal infections [4], [41]. Expanding laboratory evaluations to include serologic and molecular approaches to diagnosing infections requiring specific antimicrobial management such as the bacterial zoonoses brucellosis, leptospirosis, Q fever, and the rickettsioses adds considerable value [40]. Detection of infections of public health importance such as those caused by the arboviruses dengue, Rift Valley fever, and yellow fever can inform national control programs. Since considerable etiologic overlap exists between the syndromes of fever, acute respiratory tract infection, and diarrhea [42], [43], addressing these simultaneously in integrated sentinel studies would inform enhancements in empiric treatment guidelines and improvements in the accuracy of syndrome-based disease burden estimates. Our study had a number of limitations. While we examined a wide range of etiologies of fever, a large proportion of patients were undiagnosed suggesting that we failed to identify potentially important infections. The undiagnosed group is being investigated further using pathogen discovery approaches. Some of the diagnostic tests used in our study are less than 100% sensitive and specific and we did not test for every known pathogen. As a consequence, we probably underestimated the prevalence of some infections while misclassifying others that were falsely positive. Because a number of our diagnostic tests relied on the demonstration of a four-fold rise in antibody titer between the acute and convalescent serum sample, not all enrolled patients returned for collection of convalescent serum to have diagnoses confirmed. It follows that calculation and comparison of case fatality rate was not possible since those who died before the convalescent visit could not be confirmed cases. Incomplete diagnostic information meant that we had to extrapolate prevalence from the tested population to the untested population, potentially introducing bias. Similarly, instances of apparent infection with multiple agents were not accounted for in presentation of pie graphs. Inclusion of a well control group would have allowed the calculation of attributable fractions for individual pathogens, something that should be considered for future febrile illness research, especially in areas where malaria is endemic. Since considerable geographic variation in fever etiology is known to occur, the generalizability of our findings is uncertain. What is needed to support an integrated approach to the syndrome of fever in resource-limited areas? First, fever should be recognized alongside pneumonia and diarrhea as a major clinical syndrome of public health importance. Achieving this is likely to require leadership from international institutions of public health and reappraisal of the way that the febrile illnesses are approached in burden of disease estimates. This could include estimating total morbidity and mortality from the syndrome of fever as a first step before attributing the associated illnesses and deaths to specific etiologies, much as is done for the other major syndromes [44], [45]. Second, efforts are needed to bring together the diverse groups and disciplines currently working on the febrile illnesses to quantify the morbidity and mortality attributable to each major etiologic agent. Such integration could be facilitated by support for research efforts that study the syndrome of fever comprehensively as well as its etiologies individually, an approach that has been modeled by studies addressing the syndromes of pediatric pneumonia and diarrhea in developing countries [46], [47]. Third, improved diagnostic services are urgently needed to establish disease burden estimates and patient management for the febrile illnesses in resource-limited areas [10]. Conventional diagnostic tests for some infections, such as leptospirosis, are complex. For example, the collection of both acute and convalescent serum samples may be required, and testing services may be available at only a few national or supra-national reference laboratories. Assays relying on convalescent samples cannot be used to estimate case fatality rates [21], [26]. Conversely, simple, rapid tests applied to acute samples may have poor performance characteristics [38]. Finally, clinical studies, including clinical trials, are needed to test and improve clinical management algorithms for febrile patients. The goal should be to target antimicrobial therapy to those who need it and to avoid inappropriate use among patients who will not benefit. In this way, patient outcomes can be improved, health resources can be conserved, and disease prevention and control efforts for febrile conditions can be rationally resourced. Supporting Information Text S1 STROBE checklist. (DOC) Click here for additional data file.
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            The globalization of leptospirosis: worldwide incidence trends.

            Leptospirosis continues to be a significant zoonosis of the developing world. Globalization, in the context of international travel, particularly for recreational activities and military expeditions, has led to increased exposure of individuals from the developed world to the disease, as recent outbreaks show. We evaluated the trends in annual leptospirosis incidence for individual countries worldwide through reports from national and international organizations, the published medical literature on the subject, and web searches with the terms 'leptospirosis' and the individual country names. Inter-country variations in leptospirosis incidence, when relevant official data were available, were also analyzed. The Caribbean and Latin America, the Indian subcontinent, Southeast Asia, Oceania, and to a lesser extent Eastern Europe, are the most significant foci of the disease, including areas that are popular travel destinations. Leptospirosis is a re-emerging zoonosis of global importance and unique environmental and social correlations. Attempts at global co-ordination and recognition of the true burden of an infectious disease with significant mortality should be encouraged.
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              Impact of Environment and Social Gradient on Leptospira Infection in Urban Slums

              Introduction At present, one billion of the world's population resides in slum settlements [1]. This number is expected to double in the next 25 years [1]. The growth of large urban populations which are marginalized from basic services has created a new set of global health challenges [2],[3]. As part of the Millennium Development Goals [4], a major priority has been to address the underlying poor sanitation and environmental degradation in slum communities which in turn, are the cause of a spectrum of neglected diseases which affect these populations [2],[3],[5]. Leptospirosis is a paradigm for an urban health problem that has emerged due to recent growth of slums [6],[7]. The disease, caused by the Leptospira spirochete, produces life-threatening manifestations, such as Weil's disease and severe pulmonary hemorrhage syndrome for which fatality is more than 10% and 50%, respectively [7]–[9]. Leptospirosis is transmitted during direct contact with animal reservoirs or water and soil contaminated with their urine [8],[9]. Changes in the urban environment due to expanding slum communities has produced conditions for rodent-borne transmission [6],[10]. Urban epidemics of leptospirosis now occur in cities throughout the developing world during seasonal heavy rainfall and flooding [6], [11]–[18]. There is scarce data on the burden of specific diseases that affect slum populations [2], however leptospirosis appears to have become a major infectious disease problem in this population. In Brazil alone, more than 10,000 cases of severe leptospirosis are reported each year due to outbreaks in urban centers [19], whereas roughly 3,000, 8,000 and 1,500 cases are reported annually for meningococcal disease, visceral leishmaniasis and dengue hemorrhagic fever, respectively, which are other infectious disease associated with urban poverty [20]–[22]. Case fatality (10%) from leptospirosis [19] is comparable to that observed for meningococcal disease, visceral leishmaniasis and dengue hemorrhagic fever (20%, 8% and 10%, respectively) in this setting [20],[23],[24]. Furthermore, leptospirosis is associated with extreme weather events, as exemplified by the El Niño-associated outbreak in Guayaquil in 1998 [25]. Leptospirosis is therefore expected to become an increasingly important slum health problem as predicted global climate change [26],[27] and growth of the world's slum population [1] evolves. Urban leptospirosis is a disease of poor environments since it disproportionately affects communities that lack adequate sewage systems and refuse collection services [6],[10],[11]. In this setting, outbreaks are often due to transmission of a single serovar, L. interrogans serovar Copenhageni, which is associated with the Rattus norvegicus reservoir [6], [28]–[30]. Elucidation of the specific determinants of poverty which have led to the emergence of urban leptospirosis is essential in guiding community-based interventions which, to date, have been uniformly unsuccessful. Herein, we report the findings of a large seroprevalence survey performed in a Brazilian slum community (favela). Geographical Information System (GIS) methods were used to identify sources for Leptospira transmission in the slum environment. Furthermore, we evaluated whether relative differences in socioeconomic status among slum residents contributed to the risk of Leptospira infection, in addition to the attributes of the environment in which they reside. Methods Study site and population The study was conducted in the Pau da Lima community (Figure 1A) which is situated in the periphery of Salvador, a city of 2,443,107 inhabitants [31] in Northeast Brazil. Pau da Lima is a region of hills and valleys, which was a sparsely inhabited area of Atlantic rain forest in the 1970s and subsequently transformed into a densely-populated slum settlement (Figure 1B) due to in-migration of squatters. In total, 67% of the population of Salvador and 37% of the urban population in Brazil reside in slum communities with equal or greater levels of poverty as that found in Pau da Lima [32],[33]. 10.1371/journal.pntd.0000228.g001 Figure 1 Slum community site in the city of Salvador, Brazil. (A) The yellow line in the aerial photograph is the boundary of the study site in the Pau da Lima community. The map in the bottom left corner shows the location of Salvador in Brazil and the study site (red) within the city. (B) Photograph of the typical environment at the community study site, which shows a valley in which households is situated and the proximity of households to open sewers and refuse. (C) Close-up view of the orthomap used to georeference households (red and black dots) and environmental attributes, such as open sewers (blue line) and refuse deposits, for the region marked as a yellow box in Panel A. The red arrow represents the direction from which the photograph in Panel B was taken. A study site was established which comprised of four valleys in an area of 0.46 km2 (Figure 1A). Active hospital-based surveillance found that the mean annual incidence of severe leptospirosis was 57.8 cases per 100,000 population at the study site between 1996 and 2001 (unpublished data). The study team conducted a census during visits to 3,689 households within the site in 2003 and identified 14,122 inhabitants. Households were assigned sequential numbers. A computer-based random number generator was used to select a list of 1,079 sample households from a database of all enumerated households. Eligible subjects who resided in sample households and had five or more years of age were invited to be a study participant. Subjects were enrolled into the study between April 2003 and May 2004 according to written informed consent approved by the Institutional Review Boards of the Oswaldo Cruz Foundation, Brazilian National Commission for Ethics in Research, and Weill Medical College of Cornell University. Household survey The study team of community health workers, nurses and physicians conducted interviews during house visits and administered a standardized questionnaire to obtain information on demographic and socioeconomic indicators, employment and occupation, and exposures to sources of environmental contamination and potential reservoirs in the household and workplace. Responses reported by subjects were used to obtain information on race. The study team evaluated literacy according to the ability to read standardized sentences and interpret their meaning. Informal work was defined as work-related activities for which the subject did not have legal working documents. The head-of-household, defined as the member who earned the highest monthly income, was interviewed to determine sources and amounts of income for the household. Subjects were asked to report the highest number of rats sighted within the household property and the site of work-related activities. The study team surveyed the area within the household property to determine the presence of dogs, cats and chickens. Geographical Information System (GIS) survey An ArcView version 8.3 software system (Environmental Systems Research Institute) database was constructed with georeferenced aerial photographs and topographic maps provided by the Company for Urban Development of the State of Bahia (CONDER). Photographs of the study site, which had a scale of 1∶2,000 and spatial resolution of 16cm, were taken in 2002. During the census, the study team identified households within the study site and marked their positions onto hard copy 1∶1,500 scale maps (Figure 1C), which were then entered into the ArcView database. A survey was conducted during the seasonal period of heavy rainfall between April and August 2003 to geocodify the location of open sewage and rainwater drainage systems. During three time points within this period, the study team mapped the sites of open accumulated refuse and measured the area of these deposits. Mean values for areas of refuse deposits were calculated and used for the analyses. Serological analysis Sera were processed from blood samples collected from subjects during house visits. The microscopic agglutination test (MAT) was performed to evaluate for serologic evidence of a prior Leptospira infection [34]. A panel of five reference strains (WHO Collaborative Laboratory for Leptospirosis, Royal Tropical Institute, Holland) and two clinical isolates [6] were used which included L. interrogans serovars Autumnalis, Canicola and Copenhageni, L. borgspetersenii serovar Ballum, and L. kirschneri serovar Grippotyphosa. The use of this panel had the same performance in identifying MAT-confirmed cases of leptospirosis during surveillance in Salvador [6],[16] as did the WHO recommended battery of 19 reference serovars [34]. Screening was performed with serum dilutions of 1∶25, 1∶50 and 1∶100. When agglutination was observed at a dilution of 1∶100, the sample was titrated to determine the highest titer. Statistical methods Information for subjects was double entered into an EpiInfo version 3.3.2 software system (Centers for Diseases Control and Prevention) database. Chi-square and Wilcoxon rank sum tests were used to compare categorical and continuous data, respectively, for eligible subjects who were and were not enrolled in the study. A P value ≤0.05 in two sided testing was used as the criterion for a significant difference. Preliminary analyses evaluated a range of MAT titers as criteria for prior Leptospira infection and found that the use of different cut-off values (1∶25–1∶100) identified similar associations with respect to the spatial distribution of seropositive subjects and risk factors for acquiring Leptospira antibodies. A titer greater or equal to 1∶25 was therefore used to define the presence of Leptospira antibodies in the final analyses. The presumptive infecting serovar was defined as the serovar against which the highest agglutination titre was directed [34]. Crude prevalence rates were reported since age and gender-adjusted values did not differ significantly from crude values. Ninety-five percent confidence intervals (CI) were adjusted for the cluster sampling of households. Kernel density estimation analysis was performed with a range of bandwidths (10–120 meters) to evaluate smoothed spatial distributions of subjects with Leptospira antibodies and all subjects. The R version 2.4.1 statistical package (R Foundation for Statistical Computing) was used to obtain estimates which were adjusted for boundary effects. The ratio of the Kernel density estimators for subjects with Leptospira antibodies and all subjects was measured to determine the smoothed population-adjusted risk distribution. A digital terrain model of topographic data was used (ArcGIS 3D Analyst Extension software) to obtain continuous estimates of altitude for the study area. The distances, calculated in three-dimensional space, of households to nearest open drainage systems and refuse deposits were evaluated as proxies of exposure to these sources of environmental attributes. Elevation of households with respect to the lowest point in the valley in which they were situated was used as a surrogate for flood risk. Generalized additive models (GAM) [35] were used to evaluate the functional form of the association between continuous variables and the risk of acquiring Leptospira antibodies. When indicated, continuous variables were categorized in multivariate analyses according to the x-intercept value observed in the plots of fitted smoothed values. We used Poisson regression [36] to estimate the effect of demographic, socioeconomic, household and workplace-related factors on the prevalence of Leptospira antibodies. A Bayesian inference approach was used which incorporated two random effects in order to account for overdispersion and cluster sampling within households. This approach has been used to estimate parameters in complex models [37] and is less sensitive to sparse data [38]. Standard non-informative prior distributions were used in models which were fitted with WinBUGS version 1.4.2 (MRC Biostatistics Unit). In multivariate analysis, all variables which had a P value below 0.10 in univariate analyses were included in the initial model. In order to address co-linearity among variables, we identified sets of covariates with the high Spearman correlation coefficients (>0.3 or 44 years, respectively). However, 8.3% (95% CI 6.2–10.5) of children 5–14 years of age had evidence for a prior exposure to Leptospira. The prevalence was higher in males than females (17.8 versus 13.6%, respectively; PR 1.32, 95% CI 1.10–1.57) (Table 1). Similar associations with age and gender were observed when MAT titers of ≥1∶50 and ≥1∶100 were used to define subjects with Leptospira antibodies. 10.1371/journal.pntd.0000228.t001 Table 1 Risk factors for Leptospira antibodies among subjects at the slum community site. Variables Leptospira antibodies PR (95% CI) Yes (n = 489) No (n = 2,682) Univariatea Multivariateb No. (%) or median (IQR) c Demographic Age, years 05–14 71 (15) 781 (29) 1.00 1.00 15–24 136 (28) 704 (26) 1.98 (1.47–2.61) 2.02 (1.50–2.69) 25–34 122 (25) 524 (20) 2.31 (1.71–3.07) 2.54 (1.86–3.41) 35–44 73 (15) 350 (13) 2.11 (1.50–2.88) 2.24 (1.59–3.08) ≥45 87 (18) 323 (12) 2.60 (1.88–3.51) 2.92 (2.10–4.00) Male gender 247 (51) 1140 (43) 1.32 (1.10–1.57) 1.38 (1.14–1.64) Socioeconomic indicators Black raced 169 (35) 724 (27) 1.35 (1.11–1.62) 1.25 (1.03–1.50) Household per capita income, US$/day 1.14 (0.39–1.88) 1.30 (0.61–2.20) 0.91 (0.85–0.97)e 0.89 (0.82–0.95)e Did not complete primary school 394 (81) 2018 (75) 1.32 (1.04–1.65) - Household factors Time of residence in household, years 8 (3–17) 7 (3–12) 1.02 (1.01–1.03)e - Level above lowest point in valley, meters 18.78 (8.59–31.05) 24.71 (13.00–36.04) 0.99 (0.98–0.99)e - Distance from an open sewer, meters 14.95 (7.34–31.00) 21.04 (8.99–38.11) 0.99 (0.99–1.00)e - Distance of household from an open sewer/lowest point in valley ≥20 m/≥20 m 158 (32) 1198 (45) 1.00 1·00 ≥20 m/ 2 rats 256 (52) 1039 (39) 1.60 (1.33–1.91) 1.32 (1.10–1.58) Dog 231 (47) 1028 (38) 1.36 (1.14–1.62) - Chicken 227 (46) 988 (37) 1.40 (1.17–1.66) 1.26 (1.05–1.51) Cat 106 (22) 406 (15) 1.44 (1.15–1.77) - Work-related exposures Informal work 157 (32) 637 (24) 1.42 (1.17–1.71) - Contact with contaminated environmentg 83 (17) 284 (11) 1.57 (1.22–1.96) - Risk occupationh 49 (10) 127 (5) 1.90 (1.37–2.51) - a Univaritate prevalence ratios (PR) and 95% confidence intervals (CI) are shown for variables which were significant (P<0.05) in the univariate analyses. b Multivariate PR and 95% CI are shown for covariates which were included in the final best fit Poisson regression model. c Numbers and percentages are shown for categorical variables. Median and interquartile range (IQR) are shown for continuous variables of per capita household income, time of residence in study household, level above lowest point in valley and distance from an open sewer and refuse deposit. d Data is missing for two non-infected subjects. e PR and 95% CI are shown for continuous data. f Data is missing for one infected and two non-infected subjects. g Reported exposure to mud, refuse, flooding water or sewage water in the workplace. h Occupation as construction worker, refuse collector or mechanic, which is associated with a workplace environment characterized by high rat infestation. Panels A and B in Figure 3 show smoothed spatial distributions of subjects with Leptospira antibodies and all subjects, respectively, according to place of residence. The population-adjusted distribution (Figure 3C) showed that risk of acquiring Leptospira antibodies clustered in areas occupied by squatters at the bottom of valleys (Figure 3D). Similar spatial distributions were observed in analyses that used higher titer values to define subjects with Leptospira antibodies (Figure S1). 10.1371/journal.pntd.0000228.g003 Figure 3 Spatial distribution of subjects with Leptospira antibodies and all enrolled subjects, according to place of residence, and environmental attributes of the community site. Panels A and B show the smoothed Kernel density distribution of subjects with Leptospira antibodies (N = 489) and all (N = 3,171) subjects, respectively, according to place of residence. The yellow-to-red gradient represents increasing density in smoothing analyses which used 40 meters as the bandwidth. Black circles show the location of subject households. Panel C shows the distribution of the population-adjusted Kernel density estimator for subjects with Leptospira antibodies which was calculated as the ratio of the estimators for subjects with Leptospira antibodies and all subjects. Panel D shows a topographic map generated by the digital terrain model. The yellow line is the level that is 20 meters above the lowest point in the four valleys within the community site. Panels E and F show the distribution of, respectively, open rainwater and sewage drainage systems and accumulated refuse according to size (m2). Univariate analysis found the risk of acquiring Leptospira antibodies to be associated with increasing age, male gender, indicators of low socioeconomic level, occupations that entail contact with contaminated environments, informal work, time of residence in the study household, and environmental attributes and the presence of reservoirs in the household (Table 1). Significant risk associations were not found for formal employment and reported sighting of rats in the workplace environment. Open rainwater drainage structures and refuse deposits were distributed throughout the site; yet open sewers were more frequently encountered at the bottom of valleys (Figure 3). The distance of household to the nearest open sewer was a risk factor, whereas a significant association was not observed for distance to an open rainwater drainage system. GAM analysis showed that the risk of acquiring Leptospira antibodies had an inverse linear association with the distance of the subject's household to an open sewer and elevation of the household from the lowest point in the valley, a proxy for flood risk (Figure 4). Increased risk was observed among subjects who resided less than a threshold distance of 20 meters to these attributes (Figure 4B and C). The risk of acquiring Leptospira antibodies had an inverse non-linear association with distance of the subject's household to an open refuse deposit (results not shown). We explored a range of dichotomization criteria and found significant risk associations when subjects resided less than 20 meters from an open refuse deposit (Table 1). This association was not influenced by the size of the refuse deposit. Subjects who reported sighting two or more rats in the household environment had increased risk of acquiring Leptospira antibodies (Figure 4D). Household per capita income had an inverse linear association with the presence of Leptospira antibodies (Figure 4A). Of note, the distance of the household to an open sewer was highly correlated (Spearmen correlation coefficient = 0.71) with household elevation (Figure S2A) since open sewers drain into the bottom of valleys. An aggregate variable, distance of household located less than 20 meters from an open sewer and lowest point in a valley, was therefore used to examine the association between open sewer and flood-related exposure and infection risk (Table 1). In contrast household per capita income was not highly correlated (Spearmen correlation coefficient = 0.16) with the elevation of the household (Figure S2B). 10.1371/journal.pntd.0000228.g004 Figure 4 Generalized additive models (GAM) of the association between the risk of acquiring Leptospira antibodies and continuous variables of (A) per capita daily household income, (B) level of household in meters above the lowest point in valley, and (C) distance in meters to the nearest open sewer, and (D) reported number of rats sighted in the household environment. The coefficient, f(infection), in the GAM model is a measure for the risk of acquiring Leptospira antibodies. In Panels A, B, C and D, the x axis intercept values, where f(infection) equals zero, were US$1.70/day, 22 meters, 22 meters and 2 rats, respectively. Multivariate analyses found that the risk for acquiring Leptospira antibodies was associated with exposures in the household environment and not in the workplace setting (Table 1). Subjects who resided less than 20 meters from an open sewer and the lowest point in the valley had a 1.42 times (95% CI 1.14–1.75) increased risk for acquiring Leptospira antibodies than those who lived 20 meters or more from these attributes. Residence less than 20 meters from accumulated refuse was associated with a 1.43 times (95% CI 1.04–1.88) increased risk. Sighting of two or more rats and presence of chickens, a marker for rat infestation, in the household were significant reservoir-associated risk factors. After controlling for age, gender and significant environmental exposures, indicators of low socioeconomic level, household per capita income (PR 0.89 for an increase of US$1.00 per day, 95% CI 0.82–0.95) and black race (PR 1.25, 95% CI 1.03–1.50) were risk factors for acquiring Leptospira antibodies (Table 1). Discussion Efforts to identify interventions for urban leptospirosis have been hampered by the lack of population-based information on transmission determinants. In this large community-based survey of a slum settlement in Brazil, we found that 15% of the residents had serologic evidence for a prior Leptospira infection. The prevalence rate of Leptospira antibodies in the study slum community was similar to that (12%) found in a city-wide survey performed in Salvador [39]. Risk factors for acquiring Leptospira antibodies were associated with exposures in the household environment. Interventions therefore need to target the environmental sources of transmission - open sewers, flooding, open refuse deposits and animal reservoirs - in the places where slum inhabitants reside. After controlling for the influence of poor environment, indicators of low socioeconomic status were found to be independently associated with the risk of acquiring Leptospira antibodies. This finding suggests that in slum communities with overall high levels of absolute poverty, relative differences in socioeconomic level contribute to unequal outcomes for leptospirosis. Leptospirosis has been traditionally considered an occupational disease, since work-related activities are frequently identified as risk exposures [9]. However slum inhabitants reside in close proximity to animal reservoirs and environmental surface waters which contain Leptospira [10]. We previously found that Leptospira infection clusters within households in slum communities in Salvador [40]. In this study, we found that after controlling for confounding, significant risk exposures were those associated with the household environment rather than workplace. As a caveat, interview-elicited responses were used to evaluate work-related exposures since GIS surveys were not performed at the sites where subjects worked. It is possible that slum residents may have had work-related risk exposures which were not detected by our survey. Nevertheless, our findings support the conclusion that the slum household is an important site for Leptospira transmission and provides the rationale for interventions that target risk exposures in this environment. The study's findings indicate that the domestic rat was the principal reservoir for Leptospira transmission in the study community. Highest agglutination titers among 89% of the subjects were directed against L. interrogans serovar Copenhageni, the serovar associated with the R. norvegicus reservoir. Reported sighting of rats is considered to be an unreliable marker of rat infestation. However we found that the number of rats sighted by residents was correlated with their risk of acquiring Leptospira antibodies (Figure 4D), indicating that rat sightings may be a useful marker of infection risk in slum communities where inhabitants are accustomed to the presence of rats. Although dogs were not found to be a risk factor, detailed investigations of Leptospira carriage in urban reservoirs need to be performed. Of note, the presence of chickens in households was a risk factor, although they in of themselves are not reservoirs. This association may reflect a rat-related exposure not accounted for by reported sightings, since rats are attracted to chicken feed and waste. Raising chickens is a widespread practice in slum communities-48% (519) of the 1079 study households raised chickens. Control of rodent reservoir populations may therefore need to incorporate measures that directly address this practice. Our findings confirm hypotheses raised by previous ecologic studies [6],[10],[11] that infrastructure deficiencies related to open sewers, flooding and open refuse deposits are transmission sources for leptospirosis in the slum environment. Furthermore, there appears to be defined areas of risk associated with open sewers and refuse deposits, which serve as habitats and sources of food for rats. Home range radius of the domestic rat varies from 30–150 meters [41],[42], but home range use decreases from the centre to the edge. GAM analysis demonstrated that slum residents had a positive risk for acquiring Leptospira antibodies when households were situated within 20 meters from open sewers and refuse deposits. In addition, infection risk increased as distances from an open sewer or refuse deposit decreased, suggesting that households which are situated closer to these foci have a higher degree of environmental contamination with Leptospira and inhabitants of these households are exposed to higher inoculum doses during infection. Molecular approaches to quantify Leptospira in environmental samples [10] will be useful in answering this question and guiding recommendations for environmental decontamination and barrier control measures which can be implemented in slum communities. In addition, GAM analysis found that residents had positive risk for Leptospira infection when their households were situated within 20 meters from the lowest point in the valley (Figure 4B). In Salvador [6],[12],[16],[40] and other urban centers [11],[13],[15],[17],[18], outbreaks of leptospirosis occur during heavy rainfall and flooding events. Slum communities are built on the poor land quality and often in areas susceptible to frequent flooding. At the study site and other slum settlements in Salvador, the water table rises up to one meter during flooding events because of inadequate rainwater drainage and blockage of drainage systems with silt and refuse. The finding that subjects had increased infection risk when their households were located within 20 meters from the lowest point in the valley suggests that this distance was a proxy for the degree of contact which residents encounter flood-related exposures in the peri-domiciliary environment. We found that in addition to attributes of the environment where slum inhabitants reside, low per capita household income and black race, an indicator of health inequality in Brazil [43],[44], were independent risk factors for Leptospira infection. The social gradient in health is a widespread phenomenon [45],[46]. Our findings, although not unexpected, are noteworthy since they suggest that differences in status contribute to unequal health outcomes in a slum community where the household per capita income was less than US$1 per day for 44% of the inhabitants. Although errors in the measurement of risk exposures and residual confounding were a possibility, the strength of the association indicates a role for social determinants in Leptospira transmission. These factors may relate to risky behaviors, such as cleaning open sewers after flooding events, or limited use of protective clothing which reduce the risk of abrasions that facilitate entry of the Leptospira spirochete [47]. Low status and lack of access to amenities and social support are features of disadvantaged communities [45] which conceivably influence risk behaviors for leptospirosis. Further research is needed to evaluate the role of social factors such that effective interventions, including health education, can be implemented at the community level. A limitation of our study was the cross-sectional design which used serologic evidence for a prior Leptospira infection as the outcome. The MAT is the standard assay used in prevalence surveys [9], yet there is not an established titer criterion for defining seropositive reactions. We previously found that a MAT titer of ≥1∶25 was a specific marker for prior Leptospira infection among slum residents from Salvador and when applied, identified household clustering of infection risk [40]. In this study, cutoff titers from 1∶25 and above identified similar risk associations. In Salvador, leptospirosis is due to transmission of a single agent, L. interrogans serovar Copenhageni [6],[28]. Titers of 1∶25, as well as higher titers, were directed against this serovar (Figure 1), indicating that this cutoff was a specific and more sensitive criteria for identifying prior infections in a region where a single serovar agent is circulating. In the study, there were more men and younger subjects among non-participating subjects than participating subjects. Crude prevalence was not different from the prevalence of Leptospira antibodies which was adjusted by the age and gender distribution of the overall study population, indicating that differences between participating and non-participating subjects may not have introduced a significant bias in the estimates. Infections may have occurred up to five years prior to the survey since agglutinating antibodies may persist for this period [48],[49]. Major interventions to improve basic sanitation were not implemented in the study community, yet the possibility that environmental exposures were modified over time can not be excluded. Migration may have affected our ability to estimate prevalence and risk associations. An on-going cohort investigation of subjects enrolled in this study found that the annual out-migration rate is approximately 12% (unpublished data). The study's findings therefore need to be confirmed in prospective studies. We found that Leptospira transmission was due to the interaction of factors associated with climate, geography and urban poverty. Since the study was performed in a single community in Salvador, Brazil, our findings may not be generalizable to other slum settings. However, a large proportion of the world's slum population resides in tropical climates similar to that in Salvador. Moreover, similar conditions of poverty and environmental degradation encountered at the study site (Figure 1B) are found in many slum settlements. In Brazil, 37% of the urban population resides in slums with equal or greater levels of poverty as found in the study community [33]. Our findings may therefore be relevant to other slum communities where leptospirosis is endemic and have increasing significance as global climate change [26],[27] and growth of the world's slum population occur in the future [1],[33]. The infrastructure deficiencies which were found to be transmission factors for Leptospira in this study can be readily addressed by improving sanitation in slum communities. Investment in sanitation is a cost-effective health intervention [50],[51]. In Salvador, a city-wide sanitation program (Bahia Azul) was recently shown to have a major beneficial impact for diarrheal disease [52]. However, as frequently encountered with large-scale sanitation projects, the Bahia Azul program did not provide coverage to the study community and many of the slum settlements in the city's periphery. Equitable access to improved sanitation is therefore essential in reducing the burden of the large number of environmentally-transmitted infectious diseases, including leptospirosis, which affects slum populations. Furthermore, the finding that the social gradient within slum communities, in addition to the unhealthy environment, contributes to the risk of Leptospira infection suggests that prevention of urban leptospirosis will need to combine approaches for improving sanitation with approaches that identify and address the social determinants which produce unequal health outcomes. Supporting Information Figure S1 Smoothed Kernel density distribution of subjects with microscopic agglutination test titres of ≥1∶25 (A), ≥1∶50 (B) and ≥1∶100 (C), according to place of residence at the study site. The yellow-to-red gradient represents increasing density in smoothing analyses which used 40 meters as the bandwidth. (2.61 MB TIF) Click here for additional data file. Figure S2 Spot plots of the relationship between elevation of household level from the lowest point in valley and distance of the household to the nearest open sewer (A) and household per capita daily income (B). Closed and open dots represent houses with at least one seropositive subject and without a seropositive subject, respectively. (1.02 MB TIF) Click here for additional data file. Alternative Language Abstract S1 Abstract translated into Portuguese by Dr. Guilherme Ribeiro. (0.03 MB DOC) Click here for additional data file.
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                Author and article information

                Journal
                Int J Environ Res Public Health
                Int J Environ Res Public Health
                ijerph
                International Journal of Environmental Research and Public Health
                MDPI
                1661-7827
                1660-4601
                16 December 2013
                December 2013
                : 10
                : 12
                : 7229-7234
                Affiliations
                [1 ]Pan American Health Organization, 525 23rd St. NW, Washington, DC 20037, USA; E-Mails: aldighsy@ 123456paho.org (S.A.); najerapa@ 123456paho.org (P.N.); galand@ 123456paho.org (D.I.G.); espinalm@ 123456paho.org (M.A.E.)
                [2 ]Health and Climate Foundation, 1425 K St. NW Suite 350, Washington, DC 20005, USA; E-Mail: michel.jancloes@ 123456gmail.com
                [3 ]Instituto Oswaldo Cruz/Fundação Oswaldo Cruz (Fiocruz), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, CEP 21045-900, Brazil; E-Mail: dbuss@ 123456ioc.fiocruz.br
                [4 ]World Health Organization, Avenue Appia 20, Geneva 1211, Switzerland; E-Mails: bertherate@ 123456who.int (E.B.); durskik@ 123456who.int (K.D.)
                Author notes
                [* ]Author to whom correspondence should be addressed; E-Mail: schneidc@ 123456paho.org .
                Article
                ijerph-10-07229
                10.3390/ijerph10127229
                3881163
                24351743
                9e547cbf-b951-46d1-80d1-f460adce9a97
                © 2013 by the authors; licensee MDPI, Basel, Switzerland.

                This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 09 December 2013
                : 09 December 2013
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