Cholera surveillance and estimation of burden of cholera.

Cholera continues to be poorly controlled in multiple epidemic and endemic areas across the globe, with estimated annual incidence of 1.3-4.0 million cases, resulting in 21,000 to 143,000 deaths worldwide in 2015. The usual approach for patient diagnosis and cholera surveillance is clinical examination of cases of acute watery diarrhea (AWD), confirmed by positive culture or polymerase chain reaction tests. Rapid diagnostic tests (RDTs) are used in regions with limited laboratory capacities but have been found to demonstrate large variations in performance, ranging in sensitivity from 58% to 100% and in specificity from 60% to 100%. Most countries rely on hospital-based surveillance of diarrheal disease to compute the cholera burden. The World Health Organization (WHO) recommends that countries assess public health events involving cholera against the International Health Regulations 2005 criteria and determine need for official notification using the standard case definition. Cholera is an often under-recognized and under reported problem because of differences in case definitions, reluctance by authorities to acknowledge and report cholera, inadequacies in hospital surveillance systems, lack of effective diagnostic tests and commonalities in clinical presentation of cholera with other AWD etiologies. The resulting gap in burden data impairs economic analysis of disease impact and identification of areas for targeted control interventions. There is an urgent need to strengthen surveillance data by supplementing reported numbers with estimates from literature reviews and data from modelling studies, developing better-performing RDTs, enhancing monitoring and evaluation processes of in-country surveillance systems, and encouraging countries to report cholera cases by "rewarding" better reporting with technical support and improved access to vaccines. It is imperative that immediate steps are taken towards strengthening surveillance and reporting systems globally, especially in cholera-prone and resource-limited areas, where it will enable countries to articulate their demand for resources more accurately.