Taking aim at cholera

In 1854, John Snow’s work on cholera in London immortalised the power of mapping as a tool for disease prevention and control. Over 160 years later, a more ambitious effort to map cholera has been reported in The Lancet. Forgoing so-called shoe leather epidemiology in favour of big data, Justin Lessler and colleagues used 279 cholera datasets covering 2283 locations in 37 countries, and cluster-level maps of access to improved water and sanitation in 41 countries, to map cholera incidence across sub-Saharan Africa at a 20 km × 20 km grid scale. They merged this incidence grid with census data and subnational administrative borders to identify and rank districts by their mean annual cholera incidence. Based on these analyses, they estimate that 151 of 3751 districts (4·0%, 95% credible interval [CrI] 1·7 to 16·8) in sub-Saharan Africa, home to 87·2 million people (95% CrI 60·3 million to 118·9 million), can be classified as high incidence (>1 case per 1000 people), and that targeting just 35·3 million people (95% CrI 26·3 million to 62·0 million) in the highest incidence districts with proven interventions—safe water, sanitation, and cholera vaccination—could reduce mean annual cholera incidence in the entire region by 50%. Alternatively, targeting 50·8 million people (95% CrI 39·7 million to 62·8 million) in just five countries (Somalia, Nigeria, Democratic Republic of the Congo, Sierra Leone, and Ghana) could prevent over 38% of all regional cholera cases. These encouraging results provide a region-wide geospatial roadmap to guide the actions described in WHO and partners’ Ending Cholera: a Global Roadmap to 2030, released by the Global Task Force on Cholera Control in 2017. Lessler and colleagues show that highburden cholera hot spots to target with interventions can be identified in each affected country. Furthermore, they suggest that this strategy will yield high returns on the resources invested. The latter is particularly important given constraints on the resources needed. Sustainable water supply, sanitation, and hygiene (WaSH) infrastructure is crucial for ending transmission of cholera and other diseases transmitted by the faecal– oral route, and is a Sustainable Development Goal 2030 target in its own right, but its construction is costly and time consuming. Oral cholera vaccines, which are effective at reducing cholera transmission in the short term (3–5 years), remain in short supply relative to global demand despite substantial success in increasing their production and accessibility. In sub-Saharan Africa—an area of around 24 million km2 that is home to more than 1 billion people—cholera has been reported to WHO every year since 1971. It lags behind other regions in population coverage with improved water and sanitation, and populations in many African nations are besieged by other public health threats that increase the risk of cholera transmission and deaths, including drought or flooding; terrorism, civil conflict, or war; malnutrition; and acute economic crises or chronic poverty. Similar conditions afflict cholera-affected areas in the Middle East, Asia, and the Caribbean, with refugees from nearby countries sometimes forced to flee to cholera-endemic areas. Efforts to combat cholera in sub-Saharan Africa in the 21st century have been almost entirely reactive— focused on outbreak response through emergency WaSH measures and the occasional cholera vaccine campaign. Although cholera surveillance, reporting, and diagnostic capacity have benefited from investments in public health preparedness and training, and from a few cholera-specific projects, an overarching strategy to most effectively mobilise efforts and resources for cholera prevention has been sorely lacking. As other disease control programmes have shown, the ability to identify and target high-incidence hot spots is a For more on the cholera risks posed to refugees see http://www.icddrb.org/newsand-events/ news?id=836&task=view Published Online March 1, 2018 http://dx.doi.org/10.1016/ S0140-6736(18)30543-9