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Suspected cholera cases can be reported to health authorities from a variety of data sources including health centres or posts, hospitals, laboratories, community health workers, and other non-health sources such as teachers, religious leaders and local leaders. Informal sources such as the media and rumours may also be sources of information. All sources should be systematically tracked and further investigated to determine whether reports of suspected cases or outbreaks are accurate.
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Whatever the source of the information, when suspected cholera cases are detected or reported in a previously unaffected area, a cholera alert should be triggered, and immediate field investigation should be conducted to verify the alert and confirm the outbreak.
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Community-based active surveillance can be initiated or strengthened in at-risk areas with known seasonal upsurges and recurrent outbreaks before the expected season arrives to detect the first cholera cases as early as possible.
Acute Watery Diarrhoea
Acute watery diarrhoea is an illness characterized by three or more loose or watery (non-bloody) stools within a 24-hour period.
Suspected Cholera Case
- In areas where a cholera outbreak has not yet been declared, any person aged 2 years or older presenting with acute watery diarrhoea and severe dehydration or dying from acute watery diarrhoea.
- In areas where a cholera outbreak has been declared, any person presenting with or dying from acute watery diarrhoea.
Note: Children under 2 years of age can be affected by cholera and need to be treated immediately. When a cholera outbreak has been declared, children under 2 years of age who meet the cholera case definition should be recorded in the register, reported to the surveillance unit and considered in the epidemiological analysis.
Cholera Alert
A cholera alert (suspected cholera outbreak) is defined by the detection of at least one of the following:
- two or more people aged 2 years or older with acute watery diarrhoea and severe dehydration, or dying from acute watery diarrhoea, from the same area, within 1 week of one another;
- one death from severe acute watery diarrhoea in a person aged 5 years or older; and/or
- one case of acute watery diarrhoea testing positive for cholera by rapid diagnostic test (RDT) in an area that has not yet detected a confirmed case of cholera (including areas at risk for extension from a current outbreak).
Health facilities and community health workers should immediately report any cholera alert to the next level. The district health authorities shall then initiate a field investigation to confirm the cholera outbreak and implement control measures see section 2 – outbreak confirmation.
For additional definitions, see appendix 1 – Definitions.
Use of Cholera Rapid Diagnostic Tests (RDTs)
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RDTs do not replace stool culture or polymerase chain reaction (PCR) to confirm cholera.
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A cholera outbreak can only be confirmed when specimens from suspected cases test positive by culture or PCR at the reference laboratory.
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RDTs are intended to be used at peripheral healthcare levels only for early outbreak detection—as a tool for initial alert—and not for individual diagnosis.
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Clinical management of patients is guided by their degree of dehydration, regardless of RDT result.
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The use of RDTs in outbreak detection is limited to improving the reliability and timeliness of cholera alerts.
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RDTs also permit the triage of specimens to be tested at the laboratory. Samples testing positive on a RDT should be prioritized for laboratory testing.
Investigation of the Alert, Risk, Needs Assessments, and Initial Response
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Send a multidisciplinary team to the field to investigate every cholera alert to confirm or rule out the outbreak, assess the risk of spread, identify priority actions, conduct an initial needs assessment and implement initial control measures (see appendix 2 – field investigation and initial response checklist).
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It is important to deploy a multidisciplinary team quickly, preferably within 24 hours.
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Ideally teams should include a clinical specialist with experience in case management of cholera patients, an epidemiologist, a water and sanitation expert, an infection prevention and control expert, an expert in social mobilization, community engagement and risk communication and a laboratory technician for stool collection from suspected cases and to support and train local laboratory staff.
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Whatever the composition of the team, members should be aware of the procedures to confirm or rule out the outbreak and the elements to investigate, and should adopt a multidisciplinary approach.
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The team should work quickly and report findings, including risks and assessed needs, to decision makers as quickly as possible in order to provide a rapid and focused response.
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Teams should carry enough supplies to collect and transport stool samples, supplies to treat any patients present on site, ensure basic infection prevention and control (IPC) measures in the treatment centre and conduct community water, sanitation and hygiene (WaSH) investigations. Guidelines, protocols and information, education and communication (IEC) materials should also be taken and left in the field.
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Assess the risk of spread, magnitude and potential impact of the outbreak.
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Likelihood of transmission is based on factors such as access to safe water and improved sanitation; population behaviour (including water sources used, chlorination, open defecation, handwashing); geographical, environmental and climate conditions (expected cholera season, expected weather patterns, flooding, drought); areas with high population density (slums, camps for refugees or internally displaced persons [IDPs]), and areas with high transit of people or an influx of travellers.
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Potential impact of the disease is based on factors including existing cholera preparedness, access to treatment (oral rehydration solution [ORS] and intravenous [IV] fluids), capacity of healthcare workers to provide case management, supplies available, healthseeking behaviour, malnutrition status and population immunity, as determined by previous exposure to cholera or previous cholera vaccination.
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Identify the available resources (human and supplies) and estimate the needs based on the risk assessment.
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Communicate these estimates quickly to local and national authorities so that the necessary resources can be rapidly procured and/or provided by the government or partners.
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Calculate the supplies needed based on the expected attack rates (ARs) and the population (see appendix 3 – district-level supply forecasting tool).
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In rural communities with low population density, the ARs might vary (0.1–2%).
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In crowded places (such as urban settings and camps for internally displaced persons and refugees), the ARs tend to be higher (1–5%).
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The above actions can be taken before an outbreak is confirmed or declared.
For additional Information:
- Interim Guidance Document on Cholera Surveillance. Global Task Force on Cholera Control-Surveillance Working Group. June 2017.Click here
- Interim Technical Note. The Use of Cholera Rapid Diagnostic Tests. lobal Task Force on Cholera Control-Surveillance Working Group. November 2016.Click here
- Technical Guidelines for Integrated Disease Surveillance and Response in the African Region. Second Edition. 2010.Click here
- Early detection, assessment and response to acute public health events. World Health Organization. 2014.Click here
