INVESTIGATION OF AN OUTBREAK Dr. Nadia Aziz C.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 of the 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 diagnosis Initial 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 diagnosis A 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 diagnosis The 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 outbreak An 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 as baselines.

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, information on possible source contacts may be sought. This information is best recorded on specially prepared record forms.

Identify affected persons and their characteristics Identify additional cases Initial 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 risk The 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 outbreak Determine 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 the estimated 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

Quiz 1 What are the diseases requiring investigation?

Quiz 2 What are the steps of outbreak investigation? (enumerate at least 4 steps)