Seroprevalence of Chikungunya Virus in a Rural Community in Brazil

Abstract

Background

The emergence of the Chikungunya virus (CHIKV) is currently expanding. In 2015, 38,332 cases of Chikungunya were reported to the Brazilian epidemiological surveillance system. Eighteen months after notification of the first case in the city of Feira de Santana, we conducted the first serosurvey to define the magnitude of transmission in a rural community in Brazil.

Methodology/Main findings

The serosurvey was conducted in a random sample of 450 residences in the Chapada district, located 100 kilometers from Feira de Santana. We administered questionnaires and tested 120 sera from Chapada district residents for CHIKV IgM- and IgG-specific antibodies. An individual with CHIKV infection was defined as any person with CHIKV IgM or IgG antibodies detected in the serum. One Hundred cases of Chikungunya were reported after prolonged rainfall, which reinforced the relationship between the rainfall index and CHIKV transmission. Eighteen months after the start of the outbreak, we identified a seroprevalence of 20% (95% CI, 15.4–35%). CHIKV IgG- and IgM-specific antibodies were detected in 22/120 (18.3%) and 6/120 (5.0%) individuals, respectively. Among seropositive patients, 13/24 (54.2%) reported fever and joint pain over the previous two years (p<0.01). The rate of symptomatic CHIKV infection was 40.7%.

Conclusions/Significance

We identified a moderate seroprevalence of Chikungunya in the Chapada district, and in half of the confirmed CHIKV infections, patients reported arthralgia and fever over the previous two years.

Author Summary

The Chikungunya virus (CHIKV) epidemic is currently expanding. In 2015, 38,332 cases of Chikungunya were reported to the Brazilian epidemiological surveillance system. To date, no serosurvey has described the impact of the disease on rural communities in Brazil. We conducted a survey in which households in the Chapada district, located in Riachão do Jacuípe in Bahia, were randomly selected for serum collection to perform a CHIKV antibody test. More than 100 cases of Chikungunya were reported in the Chapada district following a three-month period of rain. Eighteen months after the start of the outbreak, we identified that 20% of the population had acquired CHIKV, and 13/24 (54.2%) reported fever and joint pain over the previous two years. The rate of symptomatic CHIKV infection was 40.7%. We identified a moderate seroprevalence of Chikungunya in the Chapada district, and half of the patients reported arthralgia and fever over the previous two years.