A Multi-Partner Consortium for Sustainable Cholera Surveillance
Agence de Médecine Préventive (AMP) launched the African Cholera Surveillance Network (Africhol) in 2009 with funding from the Bill & Melinda Gates Foundation. The project’s overall objective was to collect data for evidence-based decisions on cholera prevention in Africa and the world. Africhol’s primary aim, therefore, was to better define cholera burden, geographic distribution, seasonal patterns, and risk groups to inform prevention strategies, including immunization.
To achieve this goal, the project, which ended in 2016, successfully built a consortium of national and international organizations to implement and sustain a multi-site cholera surveillance network in 11 African countries: Cameroon, Côte d'Ivoire, Democratic Republic of the Congo (DRC), Guinea, Kenya, Mozambique, Nigeria, Tanzania, Togo, Uganda, and Zimbabwe. The surveillance network was then able to collate evidence for cholera prevention and control measures (including vaccine adoption).
Africhol also strengthened countries’ national capacity in outbreak investigations by reinforcing existing surveillance systems, and in national laboratories by providing material and training. To accomplish this, the project worked within existing national surveillance systems to implement a protocol for data collection and analysis. The common protocol for all participating countries ensured that the data collected was standardized and comparable between all countries.
Through the network, scientific information on cholera disease burden and incidence was gathered and shared with partners, countries, and the scientific community, and contributed towards improving the understanding of the dynamics of epidemics and enabling decision makers to determine the most appropriate interventions.
Strengthening Cholera Response
By 2015 the network had grown to 24 surveillance and outbreak sites, with Africhol assisting participating countries by:
- Expanding their laboratory capacities for routine confirmation of suspected cholera cases;
- Investigating affected households and nearby vicinities (to identify additional cases);
- Assessing clinical cases within specified surveillance zones to provide incidence data;
- Conducting outbreak investigations to expand knowledge of the different epidemiological contexts in which cholera occurs; and
- Conducting environmental investigations to learn more about the relationship between endemic and epidemic cholera and environmental triggers.
- Presented the first data from prospective multi-country cholera surveillance in Africa. It is the only such data based on culture confirmation and that includes a description of clinical presentation.
- Shown how confirmed cholera cases varied over time by setting.
- Identified three epidemiological patterns that can guide the decision-making processes.
- Documented that reliance on suspected cases – as is usually done in national surveillance – rather than confirmed cases can substantially overestimate cholera incidence.
- The surveillance strategy of using case-based reporting and a standard comprehensive case reporting form provided more information on at-risk populations and geographical hot spots than is currently available in the literature; this is turn should facilitate development of efficient preventive strategies.
- Identification of three epidemiological patterns of cholera in surveillance sites:
- Those with confirmed cases throughout the year such as Goma (DRC). By contrast, sustained occurrence of confirmed cases may result from ongoing environmental source contamination from which a continuously renewed susceptible, non-immune population is infected; this may have occurred in Goma, which has experienced several waves of immigration due to regional conflicts.
- Those with sporadic cases plus additional outbreaks at irregular intervals such as in Lome (Togo), Mbale (Uganda), and Conakry (Guinea). The presence of sporadic cases without ensuing outbreaks may occur from occasional introduction of infected persons into a low risk community, e.g., a community with recent cholera and a high degree of population immunity or a community with good water and sanitation infrastructure.
- Those with a history of recurrent cholera epidemics but no cases during the surveillance period, such as Beira (Mozambique) or Abidjan (Cote d’Ivoire).
- We found that most cholera cases occurred during the rainy season. However, the presence of cases before the rains start suggests that the rainy season may amplify outbreaks. Substantial precipitation can cause flooding and subsequent mixing of drinking water (pond, well, lake, river) with sewage in areas with poor sanitation. Alternatively, the rainy season may trigger human movement, such as the seasonal migration of fishermen along the West African coast or in interior lakes.
- Findings suggest that confirmed cholera burden is substantially lower than that reported from previous studies based on suspected cholera cases, and that incidence varies substantially over time and place. Efficient use of resources, such as vaccines, could be enhanced by better definition of cholera hot-spots, community behaviors that contribute to cholera spread, and high risk populations, particularly those likely to contribute to seasonal cholera spread.