Materials and methods
Study Site
Surveillance was conducted in administrative areas (currently 8) designated as “Divisions” (Bibhag) with a total of 64 districts (Zilla) and 492 subdistricts (Upazila). In May 2014, the icddr,b and the Institute of Epidemiology, Disease Control, and Research (IEDCR) collaboratively started the diarrheal disease surveillance in 10 hospitals. Surveillance was interrupted between January and May 2016 due to a gap in funding. From May 2016, surveillance was expanded to additional 12 facilities focusing on cholera surveillance. A total of 22 surveillance sites (13 districts, 6 subdistricts, 2 tertiary-level hospitals, and the Bangladesh Institute of Tropical and Infectious Disease [BITID]) were established across 21 different districts (Figure 1). We selected sentinel surveillance sites based on reports of acute watery diarrhea and cholera (including analyses of data from the national District Health Information Software v2 database) from the Directorate General of Health Services and previously published cholera surveillance studies \citep{Sack2003}.