Abstract
SummaryBackgroundIn war-torn Yemen, reports of confirmed cholera started in late September, 2016. The disease continues to plague Yemen today in what has become the largest documented cholera epidemic of modern times. We aimed to describe the key epidemiological features of this epidemic, including the drivers of cholera transmission during the outbreak.MethodsThe Yemen Health Authorities set up a national cholera surveillance system to collect information on suspected cholera cases presenting at health facilities. Individual variables included symptom onset date, age, severity of dehydration, and rapid diagnostic test result. Suspected cholera cases were confirmed by culture, and a subset of samples had additional phenotypic and genotypic analysis. We first conducted descriptive analyses at national and governorate levels. We divided the epidemic into three time periods: the first wave (Sept 28, 2016, to April 23, 2017), the increasing phase of the second wave (April 24, 2017, to July 2, 2017), and the decreasing phase of the second wave (July 3, 2017, to March 12, 2018). We reconstructed the changes in cholera transmission over time by estimating the instantaneous reproduction number, Rt. Finally, we estimated the association between rainfall and the daily cholera incidence during the increasing phase of the second epidemic wave by fitting a spatiotemporal regression model.FindingsFrom Sept 28, 2016, to March 12, 2018, 1 103 683 suspected cholera cases (attack rate 3·69%) and 2385 deaths (case fatality risk 0·22%) were reported countrywide. The epidemic consisted of two distinct waves with a surge in transmission in May, 2017, corresponding to a median Rt of more than 2 in 13 of 23 governorates. Microbiological analyses suggested that the same Vibrio cholerae O1 Ogawa strain circulated in both waves. We found a positive, non-linear, association between weekly rainfall and suspected cholera incidence in the following 10 days; the relative risk of cholera after a weekly rainfall of 25 mm was 1·42 (95% CI 1·31–1·55) compared with a week without rain.InterpretationOur analysis suggests that the small first cholera epidemic wave seeded cholera across Yemen during the dry season. When the rains returned in April, 2017, they triggered widespread cholera transmission that led to the large second wave. These results suggest that cholera could resurge during the ongoing 2018 rainy season if transmission remains active. Therefore, health authorities and partners should immediately enhance current control efforts to mitigate the risk of a new cholera epidemic wave in Yemen.FundingHealth Authorities of Yemen, WHO, and Médecins Sans Frontières.
Highlights
Yemenis continue to endure the devastating consequences of the war that erupted in March, 2015
Between Sept 28, 2016, and March 12, 2018, 1 103 683 suspected cholera cases and 2385 deaths were reported through the cholera surveillance system, representing an overall attack rate of 3·69% and a case fatality risk (CFR) of 0·22%
During the 4 weeks preceding the start of the second wave, 998 suspected cholera cases were reported in 11 governorates
Summary
Yemenis continue to endure the devastating consequences of the war that erupted in March, 2015. While this conflict has officially caused at least 8757 deaths among civilians and injured more than 50 000 people, its broader impact has severely disrupted society and infrastructure.[1 3] million people have been displaced and the health system has lost capacity to provide even basic services, with 55% of health facilities being no longer fully functional.[2] with damaged water supply infrastructure, chronic water scarcity, and surging water prices, the UN Office for the Coordination of Humanitarian Affairs estimates that more than 50% of the 29·9 million Yemenis are in need of water and sanitation assistance.[3,4] Against the backdrop of this crisis, the largest reported cholera epidemic to date is increasing the suffering of this vulnerable population. Inadequate preparedness has determined much of the mortality burden associated with cholera during some of the largest contemporary epidemics.[7,8,9]
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