Module 7: Outbreak Investigation & Disease Control

Module 7:Outbreak Investigation & Disease Control

Developed through the APTR Initiative to Enhance Prevention and Population Health Education in collaboration with the Brody School of Medicine at East Carolina University with funding from the Centers for Disease Control and Prevention

Outbreak Investigation

Acknowledgments

APTR wishes to acknowledge the following individuals that developed this module:

Kristina Simeonsson, MD, MSPHDepartment of Public HealthBrody School of Medicine at East Carolina University

Julie Daugherty, MPHDepartment of Public HealthBrody School of Medicine at East Carolina University

This education module is made possible through the Centers for Disease Control and Prevention (CDC) and the Association for Prevention Teaching and Research (APTR) Cooperative Agreement, No. 5U50CD300860. The module represents the opinions of the author(s) and does not necessarily represent the views of the Centers for Disease Control and Prevention or the Association for Prevention Teaching and Research.

Foodborne Outbreaks in the News

Presentation Objectives

1. Define the terms outbreak, epidemic and pandemic2. Discuss reasons that outbreaks occur3. Understand the rationale for investigating

outbreaks4. Describe the steps of an outbreak investigation

Is Their a Difference between an Epidemic and an Outbreak? EPIDEMIC

Occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time

OUTBREAK Epidemic limited to localized increase in the incidence of

disease CLUSTER

Aggregation of cases in a given area over a particular period without regard to whether the number of cases is more than expected

What is a Pandemic?

An epidemic occurring over a widespread area and usually affecting a substantial proportion of the population

Influenza Severe acute respiratory syndrome (SARS) Tuberculosis Acquired immunodeficiency syndrome (AIDS)

http://www.cdc.gov/ncidod/osr/site/about/graph.htm

AGENT

ENVIRONMENTHOST

• Change in susceptibility• Factors that increase exposure

• Conducive to interaction between host and agent

• Increase in amount or virulence

• Introduction into setting where it has not been before

TRAN

SMIS

SION• Enhanced mode of

transmission

Why Investigate Outbreaks?

Prevention and control Research Public concern Political interest Program considerations Training

http://www2a.cdc.gov/TCEOnline/

Steps of an Outbreak Investigation

1. Establish existence of an outbreak2. Verify the diagnosis3. Define a case4. Identify additional cases5. Perform descriptive epidemiology6. Develop and test hypothesis7. Reconsider hypothesis8. Perform additional studies if needed9. Implement control measures10. Communicate findings



Establish Existence of Epidemic

Determine if observed numbers exceed the expected level

Be aware of artifactual causes of increases or decreases of reported cases Change in reporting practices Change in case definition New diagnostic test available



Verify the Diagnosis

Confirm clinical diagnosis with laboratory techniques Not every reported case needs to be laboratory

confirmed



Case Definition

Consists of standard elements Clinical information Time Place Person

Can have varying degrees of certainty Suspect Probable Confirmed

http://www.cdc.gov/osels/ph_surveillance/nndss/casedef/measles_2010.htm

Case Definition

Can vary depending on the purpose Characterize the extent of the outbreak Determine risk factors or find a cause



Identify Additional Cases

http://www.cdc.gov/excite/classroom/outbreak/steps.htm



Perform Descriptive Epidemiology

Orient data in terms of time Orient data in terms of place Orient data in terms of person

Orient by Time

Characterize the cases by plotting a graph or epidemic curve that shows the number of cases (y-axis) over the time of onset of illness (x-axis) using an

appropriate interval

Epidemic Curve

Size of the epidemic Relationship to endemic

cases Outliers Time course Pattern of spread Where you are in the

course of the epidemic

http://www.cdc.gov/excite/classroom/legionnairesq.htm

Epidemic Curve of HUS CasesGermany 2011

http://www.eurosurveillance.org

http://www.wpro.who.int/NR/rdonlyres/7165D4BF-D820-4CB5-A1FD-267F905639D8/0/Slide1.jpg

Orient by Place

Geographic distribution of cases can provide clues to source of the epidemic Water supplies Air flow patterns in buildings Ecologic habitat of vectors

May help identify the vehicle or mode of transmission

http://gamapserver.who.int/mapLibrary/Files/Maps/Global_H5N1inHumanCUMULATIVE_FIMS_20110316.png

Orient by Person

Examine characteristics of cases Personal characteristics Exposures

http://www.wpro.who.int/sites/csr/data/data_Graphs.htm



Develop and Test Hypothesis

Develop hypothesis using descriptive epidemiology Person, place and time Clinical and laboratory findings

Test hypothesis using analytic epidemiology Identify exposures significantly associated with

illness Analytic epidemiologic study designs

▪ retrospective cohort study▪ case-control study

(Retrospective) Cohort Study

Enrolled after the disease has occurred

Enrolls everyone in a given population regardless of disease status

Technique of choice for acute outbreak in well-defined population Church picnic

(Retrospective) Cohort Study

Directly measure risk of disease because the population at risk is known

Outcome measure is relative risk Risk in the exposed group divided by the risk in the

unexposed group (relative risk) Also known as the attack rate ratio

Case-Control Study

Begins conceptually with disease and looks backward at prior exposures

Useful when the population at risk is unknown

Group of people with disease (cases) and group of people without disease (controls) are enrolled and prior exposures are ascertained Differences in exposure between groups indicates

an association between exposure and disease

Case-Control Study

True size of exposed and unexposed groups is unknown No denominator to calculate attack rate or relative risk

Outcome measure is odds ratio (OR) Odds of developing disease based on exposure

Odds ratio can approximate relative risk When the cases are representative When the controls are representative When the disease being studied is rare

Study Design Comparison

Cohort Case-Control

Illness occurs within a well-defined population

Illness does not occur in a well-defined population

Compares rates of illness among those with risk factor and those without risk factor

Compares exposures among people with illness and those without illness

Relative risk (RR) Odds ratio (OR)



Reconsider Hypothesis

“Square” the hypothesis to clinical, laboratory and epidemiologic facts

If exposure histories for ill versus well are not significantly different, develop a new hypothesis



Perform Additional Studies

Find more cases Define better the extent of the epidemic Evaluate new laboratory method Evaluate case-finding technique

Improve sensitivity and specificity of case definition

Degrees of exposure / dose response Environmental investigation



Implement Control Measures

Prevent exposure Prevent infection Prevent disease Prevent death

Control Measures for Influenza



Communicate Findings

Outbreak investigation staff Public health personnel Government officials Healthcare providers Media Community

Risk Communication

Developed from the need to find more effective ways to communicate health risks

Goal is to provide information about expected type and magnitude of an outcome from a behavior or exposure

The purpose of the message is to empower decision-making

Risk Communication Pitfalls

Mixed messages from multiple experts Messages that are over-reassuring Leaving myths, rumors, and doomsayers

unchallenged or uncorrected Public spokespersons who lack affect

http://www.bt.cdc.gov/CERC/

Emergency Risk CommunicationPrinciples

Stop trying to allay panic Emphasize there is a process in place Don’t over reassure Acknowledge uncertainty Acknowledge people’s fears Express wishes Give people things to do Acknowledge the shared misery Give anticipatory guidance Address dreaded “what if” questions Be a role model and ask more of people Be regretful

Crisis and Emergency Risk CommunicationCenters for Disease Control and Prevention, September 2002

Challenges in Outbreak Investigations Data sources Small numbers Specimen collection Publicity Reluctance to participate

Gregg Field Epidemiology 3rd edition

Summary

Steps of an outbreak investigation are a guide

Not to be used as a “one size fits all” model

Some steps may happen simultaneously

Clear and consistent communication is key

Collaborating Institutions

Center for Public Health Continuing EducationUniversity at Albany School of Public Health

Department of Community & Family MedicineDuke University School of Medicine

Advisory Committee

Mike Barry, CAELorrie Basnight, MDNancy Bennett, MD, MSRuth Gaare Bernheim, JD, MPHAmber Berrian, MPHJames Cawley, MPH, PA-CJack Dillenberg, DDS, MPHKristine Gebbie, RN, DrPHAsim Jani, MD, MPH, FACP

Denise Koo, MD, MPHSuzanne Lazorick, MD, MPHRika Maeshiro, MD, MPHDan Mareck, MDSteve McCurdy, MD, MPHSusan M. Meyer, PhDSallie Rixey, MD, MEdNawraz Shawir, MBBS

APTR

Sharon Hull, MD, MPHPresident

Allison L. LewisExecutive Director

O. Kent Nordvig, MEdProject Representative

Documents

Module 7: Outbreak Investigation & Disease Control