Taking aim at cholera
Authors: Eric Mintz
Journal: The Lancet (2018)

In 1854, John Snow's work on cholera in London immortalised the power of mapping as a tool for disease prevention and control.1Snow J On the mode of communication of cholera.2nd edn. John Churchill, London1855Google Scholar Over 160 years later, a more ambitious effort to map cholera has been reported in The Lancet.2Lessler J Moore SM Luquero FJ et al.Mapping the burden of cholera in sub-Saharan Africa and implications for control: an analysis of data across geographical scales.Lancet. 2018; (published online March 1.)http://dx.doi.org/10.1016/S0140-6736(17)33050-7Summary Full Text Full Text PDF PubMed Scopus (51) Google Scholar Forgoing so-called shoe leather epidemiology in favour of big data, Justin Lessler and colleagues2Lessler J Moore SM Luquero FJ et al.Mapping the burden of cholera in sub-Saharan Africa and implications for control: an analysis of data across geographical scales.Lancet. 2018; (published online March 1.)http://dx.doi.org/10.1016/S0140-6736(17)33050-7Summary Full Text Full Text PDF PubMed Scopus (51) Google Scholar 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 2030,3Global Task Force on Cholera ControlEnding cholera: a global roadmap to 2030.http://www.who.int/cholera/publications/global-roadmap/en/Google Scholar released by the Global Task Force on Cholera Control in 2017. Lessler and colleagues2Lessler J Moore SM Luquero FJ et al.Mapping the burden of cholera in sub-Saharan Africa and implications for control: an analysis of data across geographical scales.Lancet. 2018; (published online March 1.)http://dx.doi.org/10.1016/S0140-6736(17)33050-7Summary Full Text Full Text PDF PubMed Scopus (51) Google Scholar show that high-burden 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.4Pezzoli L on behalf of the Oral Cholera Vaccine Working Group of the Global Task ForceDeployments from the oral cholera vaccine stockpile, 2013–2017.Wkly Epidemiol Rec. 2017; 92: 437-442PubMed Google Scholar 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 1971.5WHOGlobal Health Observatory data. Number of reported cholera cases.http://www.who.int/gho/epidemic_diseases/cholera/cases/en/Google Scholar It lags behind other regions in population coverage with improved water and sanitation,6UNICEF and WHOProgress on sanitation and drinking water: 2015 update and MDG assessment.https://www.unicef.org/publications/index_82419.htmlGoogle Scholar 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;7Moore SN Azman AS Zaitchik BF et al.El Niño and the shifting geography of cholera in Africa.Proc Natl Acad Sci USA. 2017; 114: 4436-4441Crossref PubMed Scopus (35) Google Scholar terrorism, civil conflict, or war;8Kelly-Hope LA Conflict and emerging infectious diseases.Emerg Infect Dis. 2008; 14: 1004-1005PubMed Google Scholar malnutrition;9Ververs M Narra R Treating cholera in severely malnourished children in the Horn of Africa and Yemen.Lancet. 2017; 390: 1945-1946Summary Full Text Full Text PDF PubMed Scopus (4) Google Scholar and acute economic crises or chronic poverty. Similar conditions afflict cholera-affected areas in the Middle East, Asia, and the Caribbean,10Qadri F Islam T Clemens D Cholera in Yemen—an old foe rearing its ugly head.N Engl J Med. 2017; 377: 2005-2007Crossref PubMed Scopus (24) Google Scholar, 11Ivers LC Eliminating cholera transmission in Haiti.N Engl J Med. 2017; 376: 101-103Crossref PubMed Scopus (14) Google Scholar 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.12Mintz ED Tauxe RV Cholera in Africa: a closer look and a time for action.J Infect Dis. 2013; 208: S4-S7Crossref PubMed Scopus (13) Google Scholar As other disease control programmes have shown, the ability to identify and target high-incidence hot spots is a crucial element of successful strategies in resource-constrained environments. Although essential, disease mapping alone is not sufficient to guarantee the success of a control programme. Continuous iteration will be needed to maintain accurate, reliable, and up-to-date disease maps and modelling. Additionally, disease maps can aid national and local governments', partners', and donors' understanding and efforts in targeting interventions. Finally, an absence of dedicated resources for implementation of interventions beyond those available for outbreak response may hinder progress. The work by Lessler and colleagues is relevant to many parallel efforts. In support of Sustainable Development Goal 6, mapping of WaSH data will be enhanced by 2030 with more information on water quality and an additional institutional focus on schools and health facilities. Also, through its initiative on so-called precision public health, the Institute for Health Metrics and Evaluation is mapping safe water and sanitation coverage at a fine scale and has mapped child death rates in Africa by 5 km2 blocks. Recently, molecular microbiologists published a global history and geography of the seventh pandemic cholera in Africa, and suggested that extensive intercontinental spread has been accompanied by at least 11 introductions of a single expanded lineage from Asia.13Weill FX Domman D Njamkepo E et al.Genomic history of the seventh pandemic of cholera in Africa.Science. 2017; 358: 785-789Crossref PubMed Scopus (110) Google Scholar By combining epidemiological, environmental, and genomic information, maps could be generated that are capable of informing future disease prevention efforts in even more powerful ways than are currently possible. In the future, will we identify and intervene readily in high-transmission hot spots, which, like individual super-spreaders within populations, appear to amplify epidemic propagation through their social connectivity or other characteristics? Can cold spots within epidemic zones teach us anything about social behaviours, environmental conditions, or the presence of bacteriophage or other potential inhibitors of toxigenic Vibrio cholerae O1 survival in environmental reservoirs that would confer resistance to epidemic propagation? We inhabit not just a geographical space defined by distances but many different worlds within this space: the worlds of social interactions, behaviours, events, and climate, to name but a few. Disease and risk mapping help us to better understand, learn from, and more successfully navigate those worlds, and are necessary tools as we target an end to cholera. I declare no competing interests. The views in this Comment are those of the author and do not necessarily represent the official position of the Centers for Disease Control and Prevention. Mapping the burden of cholera in sub-Saharan Africa and implications for control: an analysis of data across geographical scalesAlthough cholera occurs throughout sub-Saharan Africa, its highest incidence is concentrated in a small proportion of the continent. Prioritising high-risk areas could substantially increase the efficiency of cholera control programmes. Full-Text PDF Open Access