Countdown to 2030: why we need to revisit our metrics to defeat cholera

In 2017, the Global Task Force on Cholera Control announced goals to “eliminate” cholera from more than 20 countries and reduce the number of cholera deaths by 90 percent by the year 2030.

The task force also published a roadmap proposing how to achieve these goals. The main strategies included early detection and quick response to contain outbreaks; a targeted multisectoral approach to prevent cholera recurrence, including use of oral cholera vaccine and improving water, sanitation, and hygiene (WASH) in cholera hotspots; and an effective mechanism of coordination for technical support, advocacy, resource mobilization, and partnership at local and global levels.

Now that we are nearly five years down the road, I believe it's time to review the goals, assess if they were realistic, ask if we have the right metrics to monitor progress, and if possible, determine if we are making progress toward achieving them.

First, were the goals realistic? When first announced, many experts were skeptical about the goals because it did not seem that the tools and resources were available to make a major impact on cholera incidence and mortality. After all, cholera has been endemic in Asia for centuries and has been widespread in Africa every year since 1970. Also, we lack some basic understanding about its epidemiology. Does cholera “emerge” in an area because of lack of WASH? Certainly, there are many areas in Africa and Asia where WASH indicators are poor, yet cholera is not a risk everywhere.

Rather than emerging from such areas, it seems more plausible that cholera spreads to such areas when toxigenic V. cholerae is introduced into a susceptible area as occurred in Haiti in 2010. The question then becomes what are the tools we can use to prevent this spread and is it possible to focus our efforts on stopping the spread to these susceptible areas? Improving WASH conditions everywhere in the world will certainly take longer than seven years and is not feasible by 2030.

Secondly, do we have the right metrics to accurately gauge if we're on track? An initial problem with the 2030 goals was the lack of a baseline to monitor progress. The World Health Organization has used the estimate of about 2.86 million cholera cases with 95,000 deaths annually. This estimate is similar to the estimate from IHME, of 2.88 million cases with 107,000 deaths. However, the WHO's 2019 annual report showed only 323,000 cases and 857 deaths, a fraction of the WHO estimates, mostly in Africa. But we know that many more cases go unreported in Asian countries. With major differences in our understanding of disease burden in the past, and without knowing the year-to-year cholera cases in each country, assessing progress will be very difficult. Without a useful metric, we can hope to make progress, but will not know for sure if we have.

Without reliable metrics regarding disease incidence and mortality, in what other ways is progress being made? In fact, several developments since 2017 provide optimism. These include a) increasing use of reliable rapid diagnostic tests (RDT) to quickly detect outbreaks which can speed outbreak responses; b) lab assays able to confirm cases using DNA from dried fecal samples on filter paper or from the dipstick RDT; c) development of a simple excel tool to identify cholera hotspots, helping countries focus their control efforts; d) wide-scale preventive use of oral cholera vaccine in cholera hotspots; e) increased use of genomics to identify genetic lineages to identify movement of these lineages as they move within and between countries; and f) increased emphasis on cholera control by the global community, in coordination with the Global Task Force on Cholera Control.

Given these new tools, it does seem that many of the strategies outlined in the roadmap can be used effectively; however, the strategies may require further refinement to become optimal. For example, the RDTs will need to be positioned in the districts or sub-districts, and staff must be trained to use and report results to more quickly detect outbreaks. Importantly, the relevant health ministry must be confident in the RDT results so responses to limit cholera’s spread can be initiated quickly. The increased use of RDTs, when combined with DNA confirmation, will also allow countries to understand and report their cholera statistics accurately, and this information can be used to monitor progress towards elimination.

While reactive oral cholera vaccine can be used to attempt to control outbreaks, delays in procuring and using vaccine suggest this approach has had limited effectiveness. If vaccine was available in endemic countries through national stockpiles, reactive use could have more impact. For now, preventive use of vaccine in hotspots should be emphasized. Finally, the increased use of genomics can add to our understanding of cholera’s epidemiology which will suggest new ways of control and elimination.

Cholera kills 21,000 to 143,000 people each year, and infects up to four million people worldwide. Reaching the 2030 goals will require a continued effort in detection and response, preventing recurrence via vaccine and increased WASH, and coordination of resources at local and global levels. By reviewing our goals, assessing their viability, determining metrics to monitor and measure progress, we can create – as the 2030 roadmap states – “a world in which cholera is not threat to public health.”