Control of communicable diseases standard 5: outbreak detection, investigation and response
Outbreaks of communicable diseases are detected, investigated and controlled in a timely and effective manner.
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Key indicators (to be read in conjunction with the guidance notes)
The health information system (HIS) includes an early warning component (see guidance notes 1-2).
Initiation of outbreak investigation occurs within 24 hours of notification.
The outbreak is described according to time, place and person, leading to the identification of high-risk groups.
Adequate precautions are taken to protect the safety of both individuals and data.
Appropriate control measures that are specific to the disease and context are implemented as soon as possible (see guidance notes 3-4).
Case fatality rates are maintained at acceptable levels (see guidance note 5):
- cholera: 1% or lower
- Shigella dysentery: 1% or lower
- typhoid: 1% or lower
- meningococcal meningitis: varies (see guidance note 6).
Guidance notes
1. Early warning system for infectious disease outbreaks: the key elements of such a system will include:
- case definitions and thresholds defined and distributed to all reporting health facilities;
- community health workers (CHWs) trained to detect and report potential outbreaks from within the community;
- reporting of suspected outbreaks to the next appropriate level of the health system within 24 hours of detection;
- communications systems established to ensure rapid notification of relevant health authorities, e.g. radio, telephone.
2. Confirmation of the existence of an outbreak: it is not always straightforward to determine whether an outbreak is present and clear definitions of outbreak thresholds do not exist for all diseases.
a. Diseases for which a single case may indicate an outbreak: cholera, measles, yellow fever, Shigella, viral haemorrhagic fevers.
b. Meningococcal meningitis: for populations above 30,000, 15 cases/100,000 persons/week in one week indicates an outbreak; however, with high outbreak risk (i.e. no outbreak for 3+ years and vaccination coverage <80%), this threshold is reduced to 10 cases/100,000/week. In populations of less than 30,000, an incidence of five cases in one week or a doubling of cases over a three-week period confirms an outbreak.
c. Malaria: less specific definitions exist. However, an increase in the number of cases above what is expected for the time of year among a defined population in a defined area may indicate an outbreak.
3. Outbreak control: control measures must be specifically developed to halt transmission of the agent causing the outbreak. Often, pre-existing knowledge about the agent can guide the design of appropriate control measures in specific situations. In general, response activities include:
- controlling the source. Interventions may include improving water quality and quantity (e.g. cholera), prompt diagnosis and treatment (e.g. malaria), isolation (e.g. dysentery), controlling animal reservoirs (e.g. plague, Lassa fever).
- protecting susceptible groups. Interventions may include immunisation (e.g. measles, meningitis, yellow fever), chemoprophylaxis (e.g. malaria prevention for pregnant women), improved nutrition (e.g. acute respiratory infections).
- interrupting transmission. Interventions may include hygiene promotion (e.g. for all diseases spread by the faeco-oral route), vector control (e.g. malaria, dengue).
(See also chapter 2: Water, Sanitation and Hygiene Promotion).
4. Vector control and malaria: during a malaria outbreak, vector control measures such as indoor residual spraying and the distribution of insecticide-treated bed net (ITN) programmes should be guided by entomological assessments and expertise. These interventions require substantial logistical support and follow-up that may not be available in the initial phase of the disaster. For populations that already have a high level of ITN usage (>80%), rapid re-impregnation of nets with pyrethroids may help to stem transmission (see Vector control standards 1-2).
5. Case fatality rates (CFRs): if CFRs exceed these specified levels, an immediate evaluation of control measures should be undertaken, and corrective steps taken to ensure CFRs are maintained at acceptable levels.
6. CFRs for meningococcal meningitis: the acceptable CFR for meningococcal meningitis varies according to the general context and accessibility to health services. In general, health agencies should aim for a CFR that is as low as possible, though during outbreaks it may be as high as 20%.
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