Estimating enteric fever seroincidence in Bangladesh using rapid serosurveys

BackgroundEnteric fever, caused by Salmonella Typhi or Paratyphi, is a major public health issue in low-and middle-income countries. Accurate burden estimation is hampered by limited microbiological facilities and low sensitivity of blood culture tests. Serosurveillance offers a scalable alternative to address these challenges. This study estimated the seroincidence of enteric fever in Bangladesh using cross-sectional rapid serosurveys. MethodsSchool-based surveys (January-June 2022) were conducted in Chattogram, Dinajpur, Sylhet, Satkhira, and Faridpur, and community-based surveys (July 2019-November 2021) were conducted in Dhaka and Mirzapur. Blood samples (dried blood spots or venous blood) were collected and tested for anti-Hemolysin E IgG responses using a kinetic Enzyme-linked Immunosorbent Assay. Seroincidence was estimated using a maximum likelihood approach based on peak antibody titers and decay rates, modelled from blood-culture confirmed enteric fever cases in Bangladesh. FindingsA total of 2,969 participants aged 0-22 years were enrolled, with 75.5% aged 5-15 years. Seroincidence rates (per 100 person-years) were highest in Dhaka (33.1; 95% confidence interval [CI], 29.0-37.9), followed by Mirzapur (19.5; 95%CI, 17.4-21.7) and Chattogram (17.1; 95% CI, 15.0-19.4), and the lowest in Faridpur (11.1; 95%CI, 9.6-12.7). The under 5 age group exhibited higher rates in Dhaka (40.3; 95%CI, 32.1-50.7) and Mirzapur (26.1; 95%CI, 21.0-32.4) compared to older age groups. Seroincidence was elevated in areas with higher population density. ConclusionsThis study highlights a substantial burden of enteric fever infections across Bangladesh. These provide important evidence to guide post-introduction monitoring and optimization of the typhoid conjugate vaccine program in the national immunization schedule. Key pointsThis study provides the first multi-site, rapid seroincidence estimates of typhoid and paratyphoid fever across diverse urban and rural settings in Bangladesh, revealing a substantial and previously under-recognized burden, particularly among young children. By measuring antibody responses using a targeted serologic blood test and applying a novel analytical approach based on Bangladesh-specific antibody kinetics to cross-sectional school- and community-based surveys, it addresses critical gaps left by blood culture-based surveillance, which is limited in coverage and sensitivity. Our findings demonstrate that scalable serosurveillance can reliably capture population-level transmission intensity where routine diagnostics are unavailable. These results directly inform post-introduction monitoring and optimization of the typhoid conjugate vaccine program and provide a practical framework for burden estimation and vaccine policy decision-making in other low-resource settings.