Case-Control Study of Household and Environmental Transmission of Typhoid Fever in India

Background. Typhoid fever causes substantial morbidity and mortality in low- and middle-income countries. We conducted a case-control study in Vellore, southern India, to understand risk factors for transmission of typhoid. Methods. From April 2018 to October 2019, households of blood culture-confirmed typhoid cases that occurred within a fever surveillance cohort aged 6 months-15 years, and controls matched for age, sex, geographic location, and socioeconomic status, were recruited. Information on risk factors was obtained using standard questionnaires. Household and environmental samples were collected for detection of Salmonella Typhi using real-time polymerase chain reaction. Multivariable analysis was used to evaluate associations between risk factors and typhoid. Results. One hundred pairs of cases and controls were recruited. On multivariable regression analysis, mothers eating food from street vendors during the previous week (odds ratio [OR] = 2.04; 95% confidence interval [CI], 1.03-4.12; P = .04) was independently associated with typhoid, whereas treatment of household drinking water (OR = 0.45; 95% CI, 0.25-0.80; P = .007) was protective. There was no significant difference in S Typhi detection between the environmental samples from case and control households. Conclusions. Street-vended food is a risk factor for typhoid in densely populated urban communities of Vellore. Improved sanitation facilities and awareness about point-of-use water treatment are likely to contribute to typhoid control.