Leveraging paired serology to estimate the incidence of typhoidal Salmonella infection in the STRATAA study

Serologic surveillance of at-risk populations can be used to directly estimate the incidence of typhoidal Salmonella infection across a variety of settings, including those without access to facility-based blood-culture surveillance. We collected paired blood samples approximately three months apart from an age-stratified random sample of healthy children and adults in Bangladesh, Malawi, and Nepal as part of the Strategic Typhoid Alliance Across Asia and Africa (STRATAA) study. We used a multiplex bead assay to measure the concentration of IgG antibodies against seven Salmonella typhi/paratyphi antigens (CdtB, FliC, HlyE, LPSO2, LPSO9, Vi, and YncE) in each sample and identified recently infected participants by fitting a regression mixture model to the change in IgG concentration between participants' samples. We estimated the seroincidence…