Estimating enteric fever seroincidence in rural western Cambodia: Findings from a population-based cross-sectional serosurvey

Background: Enteric fever, caused by Salmonella enterica serovars Typhi and Paratyphi, remains an important cause of febrile illness in low- and middle-income countries (LMIC). However, the exact burden is difficult to estimate due to limitations in diagnosis and surveillance.Methods: Samples from a representative cross-sectional household serosurvey in rural western Cambodia were used to estimate enteric fever seroincidence among children and young adults. Participants were enrolled between April 7 and December 10, 2023, and 529 samples from individuals aged 5-25 years were analysed. Using IgA and IgG responses to hemolysin E antigen and established models of antibody decay after infection, we estimated seroincidence, conveying the rate of new infection in the population. Participants were enrolled between April and December 2023, and 529 samples from individuals aged 5-25 years were analysed.Findings: The overall enteric fever seroincidence rate was 188·3/1,000 person-years (95%CI: 172·6, 205·5). Among children 5-15 years, it ranged between 158·2 (95%CI: 156·0, 217·4) and 254·4 (95%CI: 208·1, 311·0) across districts. Seroincidence was higher among children 5-15 years from households with unimproved drinking water sources or sanitation facilities, and districts with a higher proportion of households with unimproved WASH.Interpretation: These findings potentially support the introduction of the typhoid conjugate vaccine in rural western Cambodia. However, additional data on the relative contribution of S. Typhi versus S. Paratyphi is needed. We also demonstrate seroincidence as an adjunctive valuable surveillance tool in LMICs where facility-based surveillance may be inadequate.