Outbreak of Invasive Infections From Subtype emm26.3 Group A Streptococcus Among Homeless Adults—Anchorage, Alaska, 2016–2017

Abstract

<div class="section"> <a class="named-anchor" id="S1"> <!-- named anchor --> </a> <h5 class="section-title" id="d7328789e222">Background</h5> <p id="P1">In 2016, we detected an outbreak of group A <i>Streptococcus</i> (GAS) invasive infections among the estimated 1000 persons experiencing homelessness (PEH) in Anchorage, Alaska. We characterized the outbreak and implemented a mass antibiotic intervention at homeless service facilities. </p> </div><div class="section"> <a class="named-anchor" id="S2"> <!-- named anchor --> </a> <h5 class="section-title" id="d7328789e230">Methods</h5> <p id="P2">We identified cases through the Alaska GAS laboratory-based surveillance system. We conducted <i>emm</i>-typing, antimicrobial susceptibility testing, and whole genome sequencing (WGS) on all invasive isolates and compared medical record data of patients infected with <i>emm26.3</i> and other <i>emm</i> types. In February 2017, we offered PEH at six facilities in Anchorage a single dose of 1 gram of azithromycin. We collected oropharyngeal and non-intact skin swabs on a subset of participants concurrent with the intervention and 4 weeks afterward. </p> </div><div class="section"> <a class="named-anchor" id="S3"> <!-- named anchor --> </a> <h5 class="section-title" id="d7328789e244">Results</h5> <p id="P3">From July 2016–April 2017, we detected 42 invasive <i>emm26.3</i> cases in Anchorage, 35 of which were in PEH. The <i>emm26.3</i> isolates differed on average by only 2 single nucleotide polymorphisms. Compared to other <i>emm</i> types, infection with <i>emm26.3</i> was associated with cellulitis (odds ratio [OR] 2.5, p=0.04) and necrotizing fasciitis (OR 4.4, p=0.02). We dispensed antibiotics to 391 PEH. Colonization with <i>emm26.3</i> decreased from 4% of 277 at baseline to 1% of 287 at follow-up (p=0.05). Invasive GAS incidence decreased from 1.5 cases per 1000 PEH/week in the 6 weeks prior to the intervention to 0.2 cases per 1000 PEH/week in the 6 weeks after (p=0.01). </p> </div><div class="section"> <a class="named-anchor" id="S4"> <!-- named anchor --> </a> <h5 class="section-title" id="d7328789e264">Conclusions</h5> <p id="P4">In an invasive GAS outbreak in PEH in Anchorage, mass antibiotic administration was temporally associated with reduced invasive disease cases and colonization prevalence. </p> </div>