The cluster-randomized trial of OCV and WASH
CHOLERA
As described in detail elsewhere (9), the CRT was conducted in a densely populated urban slum in Mirpur, Dhaka. Participants were residents of households of the slum considered at higher risk of cholera by At baseline, the study area was demarcated into 90 geographical clusters with approximately the same population sizes; each cluster was separated circumferentially from adjacent clusters by a buffer zone approximately 30 m wide, intended to minimize spread of WASH messages between clusters. Prior to the OCV campaign, the clusters were block-randomized within strata defined by distance of clusters to the nearest treatment center, to one of three arms, each with 30 clusters,: an arm in which OCV was targeted to non-pregnant persons aged one year and older but no WASH intervention; an arm in which OCV was targeted to persons fulfilling same criteria and all members were targeted for the WASH intervention; and a control arm in which no intervention was delivered. Surveillance for cholera was instituted at twelve hospitals serving the study area, in which patients from the study area were identified by either census identification numbers or, if such cards were not available, identification numbers from a computerized census available at each treatment site. These unique identification numbers were used to link treatment visits to the census and thus to the identity of the treatment arm in which the patients belonged. After obtaining informed consent, physicians carried out a clinical examination and obtained fecal specimens. All fecal specimens were evaluated for 