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Concentration in
Underserved Medicine
and Public Health (UMPH)
January 2013 – June 2014
UMPH Unit #2: Practical Applications of Epidemiology

Seminar Date: To be announced. Week of April 29, 2013

Readings:
1. And The Band Played On, by Randy Shilts
2. Epidemiology definitions and information (see below)
3. “District of Columbia Municipal Regulations for Communicable and Reportable
Diseases” at http://doh.dc.gov/publication/communicable-and-reportable-diseases
4. Review some publicly available data and statistics (see list below)

Self-study objectives:
1. Define population-based measures of infectious disease including surveillance,
incidence, prevalence, mortality rate, case fatality rate, endemic, epidemic,
outbreak, cluster, and pandemic.
2. Describe how to report a “reportable disease” in Washington, DC, and how to
find local and national surveillance data.
3. Identify basic characteristics and limitations of some national surveillance
systems for health data.

Application Activity:
In his book, And The Band Played On, Randy Shilts chronicles the early days of the HIV
epidemic from the perspective of patients, physicians, scientists, public health workers,
government officials, and the public.
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Application Activity continued:
The following questions will focus our next evening seminar discussion and help guide your
reading:
1. What is the role of physicians as public health workers during an infectious disease
outbreak?
Identify specific examples from the book to fit the “Steps in an Outbreak
Investigation” as defined by the APTR and listed below.
2. What can you learn from the actions/inactions of different parts of the public health
infrastructure during the early HIV epidemic?
What are the pros and cons of conflict and of communication in disease outbreaks?
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EPIDEMIOLOGY DEFINITIONS AND INFORMATION
(Most taken from the Association of Prevention Training & Research – Population Health Module 7)
Surveillance: ongoing systematic collection, analysis, and interpretation of health data, essential
to planning, implementation, and evaluation of public health practice, closely integrated with the
timely dissemination to those who need to know. Ideally, this should be timely, complete, and
collect information on the correct population of interest.
Incidence: the number of new cases of disease developed in a given period of time divided by
the total number of people at risk in the population (susceptible). Commonly expressed relative
to a common denominator of “per 100,000 people” to allow for easy comparison.
Prevalence: the number of current cases of disease divided by the total number of at-risk people
in the population. Commonly expressed relative to a common denominator of “per 100,000
people” to allow for easy comparison
Mortality Rate: the number of people who die out of the total population in a given time period
(a type of incidence)
Case Fatality Rate: the chance of dying from a disease once it has been diagnosed; calculated as
mortality rate from a given disease divided by the incidence rate of that disease
Endemic: a constant level of a given disease in a given population (usually low-level)
Epidemic: occurrence of more cases of a disease than expected in a given area or among a
specific group of people over a particular period of time.
Outbreak: an epidemic that is limited to a localized increase in the incidence of disease.
Cluster: neither an epidemic nor an outbreak. Merely a group of cases in a given area over a
particular period without regard to whether the number of cases is more than expected.
Pandemic: epidemic occurring over a widespread area (region, continent, etc.) and usually
affecting a substantial proportion of the population. Often with high levels of morbidity and also
sometimes higher levels of mortality.
Epidemiologic triad = agent, host, environment
Why do epidemics occur? Change in any part of the triad.
- Agent: increase in the amount of agent, or the virulence of the agent, introduction of the
agent into a setting where it has not been before, transmission change (transmitted in way that is
more efficient at causing infection).
- Host: change in susceptibility (like immunosuppression), risk factors that make them more
susceptible (high-risk activities, medication use, age, exposure risk including occupational or
recreational).
- Environment: one that brings agent and host closer together.
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PUBLICLY AVAILABLE DATA AND STATISTICS
(Most via the National Center for Health Statistics [NCHS] http://www.cdc.gov/nchs/index.htm):
- U.S. Census
http://www.census.gov
- National Vital Statistics System (vital records)
http://www.cdc.gov/nchs/nvss.htm
- National Health Interview Survey (NHIS) (personal household interviews by US Census
workers, continuous, redesigned decennially)
http://www.cdc.gov/nchs/nhis.htm
- National Health and Nutrition Examination Survey (NHANES) (annual interviews and
physical exams of adults and children)
http://www.cdc.gov/NCHS/nhanes.htm
- National Ambulatory Medical Care Survey (and others of various other health care settings)
http://www.cdc.gov/nchs/ahcd.htm
- Behavioral Risk Factor Surveillance System (BRFSS) (annual telephone survey)
http://www.cdc.gov/HealthyYouth/yrbs/index.htm
- Youth Risk Behavior Surveillance System (biennial school-based survey)
http://www.cdc.gov/HealthyYouth/yrbs/index.htm
- National fatal and nonfatal violence data (several surveys and systems)
http://www.cdc.gov/injury/wisqars/index.html
- Data and Statistics for various health indicators in Washington, DC
http://doh.dc.gov/service/data-and-statistics
- Preventable Causes of Death in the District of Columbia, 2007 (DC Dept. of Health)
http://doh.dc.gov/release/district-releases-first-ever-preventable-causes-death-report
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STEPS IN AN OUTBREAK INVESTIGATION
(From APTR Module 7)
1. Establish existence of an outbreak: Determine if the observed number of cases exceeds the
expected level (versus just a cluster?). Are there other explanations for this, e.g. changes in
reporting practices, case definition changes, new diagnostic test available?
2. Verify the diagnosis: Using clinical info and labs. Labs may not be necessary for every case,
but certainly in the beginning to establish the diagnosis. Later on perhaps adequate just to verify
exposure to someone and has clinical symptoms.
3. Establish case definition: Using clinical information, exposure, lab information. May have
varying degrees of certainty – some could be “suspected cases,” “probable cases,” or “confirmed
cases.” Think about sensitivity– do you want to catch every single case at expense of false
positives (best to answer the “extent” of outbreak) – and specificity – (bets to answer the “risk
factors” for disease).
4. Identify additional cases: Be on the lookout for more cases! Either those who present
themselves or seek them out via contact tracing.
5. Perform descriptive epidemiology – Define “person” (personal characteristics of those
infected to identify risk factors), “place” (where do they live, work, eat?), and “time” (Epidemic
curve: X-axis may be hours, days, weeks. Pay particular attention to outliers to help with finding
a cause.)
http://www.cdc.gov/excite/classroom/legionnairesq.htm
6. Develop and test hypothesis – Use retrospective cohort studies (if you can study the entire atrisk population, e.g. everyone on a cruise ship; then calculate Relative Risk) or case-control
studies (if the population at risk is unknown, e.g. outbreaks across the entire US; then calculate
Odds Ratio).
7. Implement control measures: Prevent infection, or prevent morbidity/mortality if infected.
Prevention (vaccination, isolation, barrier prevention), early detection, treatment.
8. Communicate findings: to healthcare providers, to the public, to government officials. If you
are interested in media tips for risk communication, please see the “Crisis Emergency Risk
Communication” module on the CDC website.
http://emergency.cdc.gov/cerc/CERConline/index2.html
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