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The Practice of Epidemiology: An Overview. Session 1, Part 2. 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.

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The practice of epidemiology an overview

The Practice of Epidemiology: An Overview

Session 1, Part 2

Learning objectives session 1 part 2
Learning ObjectivesSession 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
OverviewSession 1, Part 2

  • Elements and specialties of epidemiology

  • Examples of epidemiology in practice

What is epidemiology
What is Epidemiology?


  • Study risk associated with exposures

  • Identify and control epidemics

  • Monitor population rates of disease and exposure

Study of distribution and determinants of states or events in specified populations, and the application of this study to the control of health problems

Key elements in epidemiology
Key Elements in Epidemiology

  • Time

    • Date / time of exposure or onset of illness

    • Seasonality of infectious diseases

    • Identifying endemic versus epidemic disease rates

  • Person

    • Age

    • Sex

    • Race or ethnicity

  • Place

    • Geographic location

    • Proximity to potential exposure

    • Clustering

Epidemiology applications

Infectious diseases

Chronic diseases


Epidemiology Applications

Epidemiology applications1




Epidemiology Applications

Epidemiology applications2




Epidemiology Applications

Epidemiology applications3

Health care


Public policy

Epidemiology Applications

Historical example of epidemiology in action

Historical Example of Epidemiology in Action

John Snow and the

Broad Street Pump

London, England


John snow 1813 1858
John Snow (1813 – 1858)

On the Mode of Communication of Cholera

Broad st pump cholera outbreak london england 1854
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

Smallpox another historical success story
Smallpox: Another Historical Success Story

Smallpox eradication workers, Nepal.

  • Viral disease

  • Spread via air droplets

  • No treatment

  • 30% fatality rate

Smallpox vaccination, Bangladesh

Photo credits; CDC Public Health Image Library

Smallpox eradication
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

Epidemiologyin Practice

Measles outbreak

Methemoglobinemia outbreak

Hurricane Isabel

Background on measles
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

  • Not endemic in the US due to high vaccination rates

Measles virion (particle)

CDC/ Cynthia Goldsmith

The beginning
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
Here Comes Trouble…

  • Infectious family members had…

    • Attended church

    • Attended parties

    • Attended family gatherings

    • Attended sports events

    • Sought health care

Public health response
Public Health Response

  • Follow-up of those exposed at different venues in 7 counties

    • 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
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
Methemoglobinemia Outbreak 2003

What is methemoglobinemia
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
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
Further Investigation

  • Punch served at the reception was identified as a potential source of the outbreak

The punch
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
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 related mortality virginia 2003
Hurricane Isabel Related Mortality – Virginia, 2003

Case study provided by Asim Jani, MD, MPH, FACP

Hurricane related deaths virginia 2003
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
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
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
References and Resources

  • 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: 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: Accessed March 1, 2012.

  • Wedding Punch Investigation Concludes [press release]. Iowa Department of Public Health. April 25, 2003.

References and resources1
References and Resources

  • 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: 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: 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: Accessed March 1, 2012.