The Research Ethics Board of Health in Bhutan and the Institutional Review Board of the Walter Reed Army Institute of Research provided ethical approval for the study. Stool samples were collected as described previously (Ruekit et al., 2014). Stool samples were collected from cases and controls, and cultured on MacConkey and Hektoen agar, and incubated overnight at 37 °C. Non-lactose-fermenting colonies were confirmed to be Shigella by standard biochemical testing; serotype was identified by O-antigen agglutination (Denka Seiken).