Session 1, Part 2
The Practice of Epidemiology:
An Overview
Learning Objectives
Session 1, Part 2
• Identify the diverse specialties in the field of
epidemiology
• Describe how epidemiological methods and
state and district public health professionals
work
Overview
Session 1, Part 2
• Elements and specialties of epidemiology
• Examples of epidemiology in practice
Elements and Applications of
Epidemiology
What is Epidemiology?
Study of distribution and determinants of
states or events in specified populations,
and the application of this study to the
control of health problems
Purposes:
• Study risk associated with exposures
• Identify and control epidemics
• Monitor population rates of disease and
exposure
Key Elements in Epidemiology
• Person
– Age
– Sex
– Race or ethnicity
• Place
– Geographic location
– Proximity to potential
exposure
– Clustering
• Time
– Date / time of exposure
or onset of illness
– Seasonality of infectious
diseases
– Identifying endemic
versus epidemic disease
rates
Epidemiology Applications
• Infectious diseases
• Chronic diseases
• Injury
Epidemiology Applications
• Social
• Nutritional
• Occupational
Epidemiology Applications
• Environmental
• Behavioral
• Forensic
Epidemiology Applications
• Health care
• Disaster
• Public policy
Historical Example of
Epidemiology in Action
John Snow and the
Broad Street Pump
London, England
1854
John Snow (1813 – 1858)
On the Mode of Communication of Cholera
Broad St. Pump Cholera Outbreak
London, England 1854
• Low-level transmission in August
• Increase of cases August 31 and
September 1
• 79 deaths on Sept. 1 and 2
• 87% of deaths clustered around
Broad St. pump
• Pump handle removed Sept. 8
The Broad Street Pump
Photo source: The John Snow Archive and Research Companion
Case List
Smallpox: Another Historical
Success Story
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•
•
Viral disease
Spread via air droplets
No treatment
30% fatality rate
Smallpox eradication workers,
Nepal.
Photo credits; CDC Public Health Image Library
Smallpox vaccination, Bangladesh
Smallpox Eradication
• Initiated in 1967
• Last naturally
occurring case in
1977
• Declared dead in
1980
• Laboratory stocks
remain in US and
Russia
Epidemiology
in Practice
Measles outbreak
Methemoglobinemia outbreak
Hurricane Isabel
Measles Outbreak
2011
Background on Measles
• Acute viral rash illness that can
cause severe pneumonia,
diarrhea, encephalitis and death
• Spreads via respiratory droplets
• One of the most highly
communicable infectious
diseases
Measles virion (particle)
CDC/ Cynthia Goldsmith
• Not endemic in the US due to
high vaccination rates
The Beginning
• June 3: Unvaccinated US resident, aged 24,
returned to Indiana from Indonesia
– Measles cases in Indonesia: ~9/100,000 population
– Patient treated for dengue
• June 20: 5 epidemiologically-linked cases
reported to Indiana State Dept of Health
• Case-finding activities revealed 8 more cases
Here Comes Trouble…
• Infectious family members had…
– Attended church
– Attended parties
– Attended family gatherings
– Attended sports events
– Sought health care
Public Health Response
• Follow-up of those exposed at different venues
in 7 counties
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Church (150 persons)
Factory (300 persons)
Bus with school-aged children
2 GP offices, 1 OB office, 1 urgent care facility, 4
hospitals or emergency rooms
• Media releases
• Statewide Health Alert Network messages to
healthcare providers
Department of Health
Recommendations
• For exposed persons without evidence of
measles
– Vaccination within 3 days of exposure, or
– Immunoglobulin within 6 days for high risk patients
• For potentially exposed healthcare personnel
– Exclude from patient care responsibilities
• For the community
– Testing and vaccination clinics
Methemoglobinemia Outbreak
2003
What is Methemoglobinemia?
• Change in hemoglobin molecule that impairs the
ability of red blood cells to carry oxygen
• Can result in headaches, shortness of breath,
nausea, increased heart rate, weakness, fatigue,
and a bluish discoloration of the skin
• Caused by ingestion or inhalation of oxidizing
agents
Wedding Reception
• Approximately 500 persons in attendance
• Attendees began to feel ill after arriving at the
reception
• Several attendees transported by ambulance to
local emergency rooms
• 83 attendees sought emergency medical care,
20 hospitalized
• Diagnosis of methemoglobinemia was made
Further Investigation
• Punch served at the reception was identified as
a potential source of the outbreak
The Punch
• Obtained frozen through a local caterer
• Caterer obtained flavor mix from out-of-state
company
• Flavor mix provided to local food processing
company where sugar and citric acid were
added
• Caterer added water and froze punch for sale
• Same lot of punch served at wedding reception
was also served at a baby shower
What Happened?
• Samples from the punch and dry mix indicated
sodium nitrite contamination (oxidizing agent)
• Sodium nitrite probably added instead of citric
acid
• Both sodium nitrite and citric acid are white
powders and both were used at the food
processing plant
Hurricane Isabel
2003
Hurricane Isabel Related
Mortality – Virginia, 2003
Case study provided by Asim Jani, MD, MPH, FACP
Hurricane Related Deaths –
Virginia, 2003
• Age range 7 – 85; 66% over age 45
• Most deaths due to drowning, fallen trees, power
outages
• 34% due to traumatic head injuries
• 28% with confirmed presence of alcohol or
drugs
• 12 deaths “direct”; 20 deaths “indirect”
Post-Hurricane Health
Concerns
Of 210 households surveyed:
• 65% without electricity
• 24% without running water
• 21% without land or cellular phone
service
• 12% without a 3-day supply of food
• 1% with hurricane-related injuries
• 5% with hurricane-related illness
• 8% require some kind of medical care
Session Summary
• Epidemiology is the study of distribution and
determinants of states or events in specified
populations
• John Snow pioneered the first epidemiologic
methods when he used person, place, and time
data
• Epidemiology specialties complement each
other in outbreak investigations and other public
health research settings
References and Resources
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Gordis L. Epidemiology. 2nd ed. Philadelphia, Pa: WB Saunders Company;
2000.
Last JM. A Dictionary of Epidemiology. New York, NY: Oxford University
Press; 1988.
Mountcastle S. Introduction to Forensic Epidemiology. FOCUS on Field
Epidemiology [serial online]. 2004:2(5). North Carolina Center for Public
Health Preparedness, University of North Carolina at Chapel Hill School of
Public Health. Available at: http://cphp.sph.unc.edu/focus/vol2/issue5/25ForensicEpi_issue.pdf. Accessed March 1, 2012.
Notes from the Field: Measles Outbreak – Indiana, June-July 2011. MMWR
Morb Mortal Wkly Rep. 2011;60(34):1169. Available at:
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6034a5.htm. Accessed
March 1, 2012.
Wedding Punch Investigation Concludes [press release]. Iowa Department
of Public Health. April 25, 2003.
References and Resources
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Pfau S. Ten Essential Public Health Services. Work Group for Health and
Development, University of Kansas; 2004. The Community Toolbox,
Chapter 2, Section 7. Available at:
http://ctb.ku.edu/en/tablecontents/sub_section_main_1804.aspx. Accessed
March 1, 2012.
St George DMM. First Responder Epidemiology Training Course [online
training]. North Carolina Center for Public Health Preparedness, University
of North Carolina at Chapel Hill School of Public Health; 2004.
Umble K with Nelson AL, Alexander LK. John Snow – Broad Street Pump
Outbreak [online case study]. University of North Carolina at Chapel Hill
School of Public Health; 2004. Available at:
http://courses.sph.unc.edu/john_snow/. Accessed March 1, 2012.
Fig 11.2: Broad Street pump, modern replica; Broadwick Street, London
[photograph]. John Snow Archive and Research Companion [Web site].
MATRIX: The Center for Humane Arts, Letters, and Social Sciences Online,
Michigan State University. Available at:
http://johnsnow.matrix.msu.edu/book_images11.php. Accessed March 1,
2012.