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
THANK YOU
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