Dr. Faisal Al HaddadConsultant of Family Medicine

Goals

The goals of this presentation are to:

Provide a general overview of the basic steps of disease outbreak investigations

Describe factors that may contribute to a decision to investigate

Outbreaks: The basics

Goals of an outbreak investigation:To identify the source of illness

To guide public health intervention

Ways to recognize an outbreak:Routine surveillance activities

Reports from clinicians and laboratories

Reports from affected individuals

Why investigate an outbreak?

Characterize a public health problem

Identify preventable risk factors

Provide new research insights into disease

Train health department staff in methods of public health investigations and emergency response

Steps of an outbreak investigation

1. Verify the diagnosis and confirm the outbreak

2. Define a case and conduct case finding

3. Tabulate and orient data: time, place, person

4. Take immediate control measures

5. Formulate and test hypothesis

Steps of an outbreak investigation

6. Plan and execute additional studies

7. Implement and evaluate control measures

8. Communicate findings

N.B. These steps may occur simultaneously or be repeated

as new information is received.

Step 1: Verify the diagnosis and confirm the outbreak

Verifying the existence of a true outbreak is critical to proceeding with an investigation.

Confirmation of the diagnosis with a laboratory is important. Without confirmation, the situation may become a “pseudo-outbreak,”

Rule out misdiagnoses or laboratory error

Step 2: Define a case and conduct case findingDevelop a specific case definition using:

Symptoms or laboratory resultsTime periodLocation

Conduct surveillance using case definitionExisting surveillanceActive surveillance (e.g. review medical

records)

Interview case-patients

Step 3: Tabulate and orient dataCreate line listing

PersonWho was infected?What do the cases have in common?

PlaceWhere were they infected?May be useful to draw a map

TimeWhen were they infected?Create an epidemic curve

Step 4: Take immediate control measures

If an obvious source of the contamination isidentified…institute control measures immediately!

Step 5: Formulate and test hypothesis

Develop hypotheses literature reviews of previous outbreaks

interviews of several case-patients

Conduct an analytic study to test hypothesesRetrospective cohort study

Case-control study

Step 6: Plan and execute additional studies

Environmental samplingCollect appropriate samples

Allow epidemiological data to guide testing

If analytic study results are conclusive, don’t wait for positive samples before implementing prevention

Step 7: Implement and evaluate control measuresPrevent further exposure and future

outbreaks by eliminating or treating the source

Work with regulators, industry, and health educators to institute measures

Create mechanism to evaluate both short- and long-term success

Step 8: Communicate findings

Identify a single member of the investigation team to interact with media and communicate progress and findings

Summarize investigation, make recommendations, and disseminate report to all participants

ConclusionsThe steps listed for an outbreak investigation

comprise a brief introduction and rough guide. Only by conducting investigations repeatedly over an entire career will public health professionals truly learn the methods of outbreak investigations.

Snow’s “shoe leather epidemiology” serves as a model of critical thinking and public health action.

QUESTION 1During the investigation of an outbreak of food poisoning at a summer camp, food histories were obtained from all campers as indicated in the following table. Which of the food items was probably responsible for the outbreak?

QUESTION 2

Which one of the following is LEAST helpful in the investigation of an outbreak of suspected food poisoning?

1. Culture of vomitus of affected persons 2. Culture of feces of affected persons 3. Rapid identification of cases 4. Collection of samples of food eaten 5. Identification of foods consumed by individuals

Online resourcesInformation for Public Health Professionals-

Investigating Foodborne Disease Outbreaks. Available online at: http://www.cdc.gov/foodborneoutbreaks/info_healthprofessional.htm

To conduct an online outbreak investigation, “Botulism in Argentina,” visit the CDC website at: http://www.phppo.cdc.gov/phtn/casestudies/computerbased/default.htm

To explore an historical outbreak investigation, visit the online UNC John Snow Case Study at: http://www.sph.unc.edu/courses/Course_support/Case_studies/John Snow

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