Burden of typhoid fever in low-income and middle-income countries: a systematic, literature-based update with risk-factor adjustment

Abstract

Background No access to safe water is an important risk factor for typhoid fever, yet risk-level heterogeneity is unaccounted for in previous global burden estimates. Since WHO has recommended risk-based use of typhoid polysaccharide vaccine, we revisited the burden of typhoid fever in low-income and middle-income countries (LMICs) after adjusting for water-related risk. Methods We estimated the typhoid disease burden from studies done in LMICs based on blood-culture-confi rmed incidence rates applied to the 2010 population, after correcting for operational issues related to surveillance, limitations of diagnostic tests, and water-related risk. We derived incidence estimates, correction factors, and mortality estimates from systematic literature reviews. We did scenario analyses for risk factors, diagnostic sensitivity, and case fatality rates, accounting for the uncertainty in these estimates and we compared them with previous disease burden estimates. Findings The estimated number of typhoid fever cases in LMICs in 2010 after adjusting for water-related risk was 11·9 million (95% CI 9·9–14·7) cases with 129 000 (75 000–208 000) deaths. By comparison, the estimated riskunadjusted burden was 20·6 million (17·5–24·2) cases and 223 000 (131 000–344 000) deaths. Scenario analyses indicated that the risk-factor adjustment and updated diagnostic test correction factor derived from systematic literature reviews were the drivers of diff erences between the current estimate and past estimates. Interpretation The risk-adjusted typhoid fever burden estimate was more conservative than previous estimates. However, by distinguishing the risk diff erences, it will allow assessment of the eff ect at the population level and will facilitate cost-eff ectiveness calculations for risk-based vaccination strategies for future typhoid conjugate vaccine