The Practice of Epidemiology: An Overview

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

OverviewSession 1, Part 2

• Elements and specialties of epidemiology

• Examples of epidemiology in practice

Elements and Applications of Epidemiology

What is Epidemiology?

Purposes:• 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• 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 PumpLondon, 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

Smallpox eradication workers, Nepal.

Smallpox vaccination, Bangladesh

• Viral disease• Spread via air droplets• No treatment• 30% fatality rate

Photo credits; CDC Public Health Image Library

Smallpox Eradication• Initiated in 1967

• Last naturally occurring case in 1977

• Declared dead in 1980

• Laboratory stocks remain in US and Russia

Epidemiologyin Practice

Measles outbreakMethemoglobinemia outbreak

Hurricane Isabel

Measles Outbreak2011

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• 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– 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 Isabel2003

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• 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/issue5/2-5ForensicEpi_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 • 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.