INVESTIGATION OF AN OUTBREAK
Dr. Nadia AzizC.A.B.C.M.
Department of community medicine
Objectives
1- Define what is an outbreak.2- Explain what are the unique aspects of the outbreak investigation.
3-Identify diseases requiring investigation.
4-Explain steps followed to contain and control the outbreak.
DEFINITIONS
Outbreak: Sudden occurrence of cases beyond expected level in relatively limited geographical area (usually limited to a small focal area)Epidemic: covers larger geographical areas& has more than one focal point.
DEFINITIONS
Outbreak epidemiology: Study of a disease cluster or epidemic in order to control or prevent further spread ofthe disease in the population.
Unique aspects of outbreak investigation
1- There is a pressure & urgency to conclude the investigations quickly that lead to hasty decision.2- Data sources are often incomplete & less accurate.
3- Decreased statistical power due to analysis of small numbers.
4- Publicity surrounding the investigation – community members may have preconceived ideas.
Diseases requiring investigation
1- Endemic diseases with epidemic potential e.g. malaria, cholera, measles, hepatitis, meningococcal meningitis.2- Even a single case of a disease for which eradication/elimination goals have been set e.g. polio.
3- Rare but internationally important diseases with high case fatality rates e.g. yellow fever.
4- outbreak of unknown etiology.
INVESTIGATION OF AN OUTBREAK
The response to an outbreak report must be management of those infected, and containment of the outbreak by interrupting transmission of the infectious agent.INVESTIGATION OF AN OUTBREAK
Steps in an outbreak response are systematic and based on epidemiological evidence despite the fact that public and political reaction, urgency and the local situation may make this difficult.Steps of outbreak investigation
The following steps are sometimes done concurrently:1- Verify the diagnosis
2- Confirm the existence of an outbreak
3- Identify affected persons and their characteristics
- Record case histories
- Identify additional cases
_ Define and investigate population at risk
Steps of outbreak investigation
4- Formulate a hypothesis as source and spread of the outbreak
5- Contain the outbreak
- Manage cases
- Implement control measures to prevent spread
6- Conduct ongoing disease surveillance
- Prepare a report.
INVESTIGATION OF AN OUTBREAK
Verify the diagnosisInitial notification of an outbreak is often made by a health worker who must collect as detailed history as possible from the initial cases.
INVESTIGATION OF AN OUTBREAK
Verify the diagnosisA tentative differential diagnosis may be made, for example food poisoning or cholera, that enables the investigator to anticipate the diagnostic specimens required and the kind of equipment to be used during the investigation.
INVESTIGATION OF AN OUTBREAK
Verify the diagnosisThe laboratory that will analyse the specimens should be
alerted at this stage. If initial cases have died, the extent and need for autopsies should be considered.
For surveillance and control purposes, investigators must agree on a common surveillance case definition (this
may not always correspond to the clinical case definition).
INVESTIGATION OF AN OUTBREAK
Confirm the existence of an outbreak
Some diseases, may remain unrecognized, new cases may come to light, for instance, when new treatments attract patients who previously relied on traditional medicines.
Such ”false outbreaks” must be excluded through attempts at determining the previous incidence or prevalence of the disease.
INVESTIGATION OF AN OUTBREAK
Confirm the existence of an outbreakAn outbreak can be demonstrated on a graph of incidence over time
and by a map of
Geographical
extension.
Confirm the existence of an outbreak
For diseases showing a cyclical or seasonal variation, the average incidence rates over particular weeks or months of previous years, may be used asbaselines.
INVESTIGATION OF AN OUTBREAK
Identify affected persons and their characteristics
Record case histories
Information about each confirmed or suspected case must be recorded to obtain a complete understanding of the outbreak.
Usually this information includes name, age, sex, occupation, place of residence, recent movements, details of symptoms (including dates and time of onset) and dates of previous immunization against
childhood or other diseases.
Identify affected persons and their characteristics
If the incubation period is known, informationon possible source contacts may be sought. This information is best recorded on specially prepared record forms.
Identify affected persons and their characteristics
Identify additional casesInitial notification of an outbreak may come from a clinic or hospital, health centres, dispensaries and villages in the area may reveal other cases, sometimes with a range of additional
symptoms.
INVESTIGATION OF AN OUTBREAK
Define and investigate population at riskThe population at risk of infection must be identified; this provides the denominator required and ensures that remaining cases can be identified.
Overall or specific attack rates (age-specific village-specific) can then be calculated.
Define and investigate population at risk
The population at risk may require laboratory investigation (e.g. rate of nasal meningococcal carriage in the population).
Microbiological typing and susceptibility to antibiotics can then be used to develop appropriate control measures.
INVESTIGATION OF AN OUTBREAK
Formulate a hypothesis as to source and spread of the outbreakDetermine why the outbreak occurred, when it did and what set the stage for its occurrence. Whenever possible the relevant conditions before the outbreak should be determined.
For foodborne outbreaks it is necessary to determine source, vehicle, predisposing circumstances and portal of entry.
Formulate a hypothesis as to source and spread of the outbreak
All links in the process must be considered:i) disease-causing agent in the population
and its characteristics.
ii) existence of a reservoir.
iii) mode of exit from this reservoir or source.
iv) mode of transmission to the next host.
v) Mode of entry.
vi) susceptibility of the host.
Formulate a hypothesis as to source and spread of the outbreak
All the links & calculations (attack rates) will lead to the development of new hypotheses .Test the hypothesis by further investigation and analysation of existing data or collection of additional data (case- control studies).
INVESTIGATION OF AN OUTBREAK
Contain the outbreak
The key to effective containment of an outbreak is a coordinated investigation and response involving health workers including clinicians, epidemiologists, microbiologists, health educators and the public health authority.
The best way to ensure coordination may be to establish an outbreak containment committee early in the outbreak.
Contain the outbreak
After the epidemiological characteristics of the outbreak have been better understood, it is possible to implement control measures to prevent further spread of the infectious agent. However, from the very beginning of the investigation the investigative team must attempt to limit the spread and the occurrence of new cases.Control Measures
Many communicable diseases can be prevented by:1- chemoprophylaxis or vaccination.
2- Immediate isolation of affected persons can prevent spread.
3- measures to prevent movement in or out of the affected area may be considered.
Control Measures
Universal precautions in patient care are essential.Whatever the urgency of the control measures they must also be explained to the community at risk.
Population willingness to report new cases, attend vaccination campaigns, improve standards of hygiene or other such activities is critical for successful containment.
Control Measures
If supplies of vaccine or drugs are limited, it may be necessary to identify the groups at highest risk initial for control measures.Control Measures
Once these urgent measures have been put in place, it is necessary to initiate more permanent measures such as health education, improved water supply, vector control or improved food hygiene.
It may be necessary to develop and implement long-term plans for continued vaccination after an initial campaign.
Conduct ongoing disease surveillance
During the acute phase of an outbreak it may be necessary to keep persons at risk (e.g. contacts) under surveillance for disease onset.After the outbreak has initially been controlled, continued community surveillance may be needed in order to identify additional cases and to complete containment.
Disease Surveillance
Sources of information for surveillance include:i) notifications of illness by health workers,
community chiefs, employers, school teachers, heads of families.
ii) certification of deaths by medical authorities.
iii) data from other sources such as public health laboratories, entomological and veterinary services.
Disease Surveillance
It may be necessary to maintain estimates of the immune status of the population when immunization is part of control activities, by relating the amount of vaccine used to theestimated number of persons at risk, including newborns.
Prepare a report
A report should be prepared at intervals during containment if possible, and after the outbreak has been fully contained.Reports may be:
i) a popular account for the general public so that they understand the nature of the outbreak and what is required of them to prevent spread or recurrence.
Prepare a report
ii) an account for planners in the Ministry of Health/local authority so as to ensure that the necessary administrative steps are taken to prevent recurrence:
iii) a scientific report for publication in a medical journal or epidemiological purposes.
Thank you
&Good Luck
with Quiz