Cholera outbreaks in sub-Saharan Africa during 2010-2019: A Descriptive Analysis
Authors: Zheng Qulu , Luquero Francisco J , Ciglenecki Iza , Wamala Joseph F. , Abubakar Abdinasir , Welo Placide , Hussen Mukemil , Wossen Mesfin , Yennan Sebastian , Keita Alama , Lessler Justin , Azman Andrew S. , Lee Elizabeth C. 
Published: October 2021

Background

Cholera remains a public health threat, but is inequitably distributed, especially affecting areas without universal access to safe water and sanitation, including much of sub-Saharan Africa. Lack of standardized reporting and inconsistent outbreak definitions limit our understanding of cholera outbreak epidemiology.

Methods

We curated a database of cholera incidence and mortality from sub-Saharan Africa from 2010 to 2020 and developed methods to reconstruct epidemic curves. We then described the distribution of key outbreak metrics, including outbreak size and duration.

Results

We identified 999 suspected cholera outbreaks in 744 unique regions across 25 sub-Saharan Africa countries, and outbreak periods accounted for 1.8 billion person-months (2% of the total during this period) from January 2010 through January 2020. Among the 692 outbreaks reported from second-level administrative units (e.g., districts), the median attack rate was 0.8 per 1,000 people (IQR, 0.3-2.4 per 1,000), the median epidemic duration was 13 weeks (IQR, 8-19), and the median early outbreak reproductive number was 1.8 (range, 1.1-3.5). Rural outbreaks had more than twice the case fatality risk than urban ones (median of 1.8% versus 0.8%). Larger attack rates were associated with longer times to outbreak peak, longer epidemic durations, and lower case fatality risks.

Conclusions

Despite reporting gaps and the limitations of analyzing outbreaks by administrative units, this work provides a baseline from which to monitor progress towards cholera control and essential statistics to inform outbreak management and emergency response in sub-Saharan Africa.

Research in context

Evidence before this study

We used PubMed to search for relevant studies published between 2010 and 2019, using the term “Cholera AND (Outbreak OR epidemic) AND (Africa OR Algeria OR Angola OR Benin OR Botswana OR Burkina Faso OR Burundi OR Cabo Verde OR Cameroon OR Central African Republic OR Chad OR Comoros OR Congo Democratic Republic of the OR Congo, Republic of the OR Cote d’Ivoire OR Djibouti OR Egypt OR Equatorial Guinea OR Eritrea OR Eswatini OR Ethiopia OR Gabon OR Gambia OR Ghana OR Guinea OR Guinea-Bissau OR Kenya OR Lesotho OR Liberia OR Libya OR Madagascar OR Malawi OR Mali OR Mauritania OR Mauritius OR Morocco OR Mozambique OR Namibia OR Niger OR Nigeria OR Rwanda OR Sao Tome and Principe OR Senegal OR Seychelles OR Sierra Leone OR Somalia OR South Africa OR South Sudan OR Sudan OR Tanzania OR Togo OR Tunisia OR Uganda OR Zambia OR Zimbabwe)”. Of 544 results, 137 were either not about cholera outbreaks or were about cholera outbreaks in a particular country or context and 407 were not about cholera outbreaks. The remaining three were a review of cholera outbreaks in Africa by Martin et al, who focused on general epidemiology and biology of cholera outbreaks before 2011; a review of epidemiology of cholera by Jacqueline et al, who explored the duration, case fatality rate, genomics, risk factors and surveillance of outbreaks across Africa before 2017; and a study of recurrent outbreaks in Africa by Abraham et al, who examined the historical trends, risk factors, burden, severity and control strategies of outbreaks by geographic regions based on available reports from January, 1970 through August, 2017. In addition, a summary table developed by Médecins Sans Frontières (MSF) for cholera outbreak management and response in the field provided major outbreak characteristics (e.g., attack rate, duration, time to outbreak peak) in rural settings, urban settings and slums, and closed situations (e.g., refugee camps) based on a review of cholera epidemics between 1990 and 1997.

Added value of this study

Previous reviews based on available outbreak reports reflect restricted summaries of outbreak characteristics. To present a comprehensive and up-to-date summary for outbreaks in sub-Saharan Africa, we examined key outbreak features by applying a systematic outbreak definition to time series from a large cholera incidence database. To our knowledge, this is the largest centralized source of global cholera incidence and mortality data. We identified 999 suspected cholera outbreaks in 744 sub-national regions across 25 countries in sub-Saharan Africa, where 2% or 1.8 billion person-months of the total population were living in regions with ongoing outbreaks in the period from 2010 through 2019. In addition, our results suggest that population density may not be universally associated with more severe outbreak outcomes. Compared to historical summaries from MSF, our estimates of attack rates and CFRs are much lower in both rural and urban settings, while the estimate of proportion of cases reported during the peak week is slightly higher, leading to only one-third to one-fourth of the previous estimation of peak bed capacity.

Implications of all the available evidence

Cholera remains a public health threat in sub-Saharan Africa. This summary of the characteristics and transmission dynamics of outbreaks occurring in sub-Saharan Africa in the period from 2010 through 2019 increases our understanding of cholera outbreak epidemiology and serves as a practical source for future outbreak management and response. As several sub-Saharan African countries have started to developed country plans to reduce cholera incidence in the coming years, our study emphasizes the importance of improving cholera monitoring and surveillance (e.g., laboratory confirmation and finer geographic scale of reporting) in order to identify finer-scale outbreaks, estimate the true burden of cholera and target interventions with limited resources.