Clinical Cholera Surveillance Sensitivity in Bangladesh and Implications for Large-Scale Disease Control

Abstract

Background: A surveillance system that is sensitive to detecting high burden areas is critical for achieving widespread disease control. In 2014, Bangladesh established a nationwide, facility-based cholera surveillance system for Vibrio cholerae infection. We sought to measure the sensitivity of this surveillance system to detect cases to assess whether cholera elimination targets outlined by the Bangladesh national control plan can be adequately measured.

Methods: We overlaid maps of nationally representative annual V cholerae seroincidence onto maps of the catchment areas of facilities where confirmatory laboratory testing for cholera was conducted, and we identified its spatial complement as surveillance greyspots, areas where cases likely occur but go undetected. We assessed surveillance system sensitivity and changes to sensitivity given alternate surveillance site selection strategies.

Results: We estimated that 69% of Bangladeshis (111.7 million individuals) live in surveillance greyspots and that 23% (25.5 million) of these individuals live in areas with the highest V cholerae infection rates.

Conclusions: The cholera surveillance system in Bangladesh has the ability to monitor progress towards cholera elimination goals among 31% of the country's population, which may be insufficient for accurately measuring progress. Increasing surveillance coverage, particularly in the highest risk areas, should be considered.

Keywords: Bangladesh; cholera; disease control; elimination; surveillance.

Figure 1.

A map of the cholera greyspots in Bangladesh. Populations living in the coral pink areas are inside the cholera surveillance zone. The gray areas are places where we have little information on clinical cases of cholera because they are not captured by the national cholera surveillance system in Bangladesh.

Figure 2.

Cholera risk map as categorized by the risk of seroincidence relative to a population-weighted mean by 5 km × 5 km grid cell (A). The map illustrates grid cells of high-, moderate-, and low-risk areas and which grid cells are captured by the cholera surveillance zone (10, 20, 30, and 30 km radius for subdistrict, district, and tertiary care, and International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) hospitals, respectively), indicated by the transparent buffers. Cholera risk map as categorized by the estimated number of Vibrio cholerae infections by 5 km × 5 km grid cell (B). The black marks indicate sentinel hospital locations, and the transparent buffers overlayed represent the cholera surveillance zone.

Figure 3.

(A) The number of people living in high-, moderate-, and low-risk areas as defined by the relative and absolute risk metrics across Bangladesh and captured in the cholera surveillance zone (shown in different shades as the geographic frame). The percentages in each bar represent the percentage of the people living in high-, moderate-, and low-risk areas across Bangladesh that are captured in the cholera surveillance zone. (B) The number of people infected with Vibrio cholerae living in high-, moderate-, and low-risk areas as defined by the relative and absolute risk metrics across Bangladesh and captured in the cholera surveillance zone (shown in different shades as the geographic frame). The percentages in each bar represent the percentage of infected people living in high-, moderate-, and low-risk areas across Bangladesh that are captured in the cholera surveillance zone.