Epidemiologic Surveillance and Outbreak Investigation

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Epidemiologic Surveillance and Outbreak
Investigation

• Presented by CPT Kathy Hughes DVM, TXSG
• Houston Med Response Group
• Texas Medical Rangers
• 23 Mar 05

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Epidemiology

• The study of diseases and health in populations
• The study of the distribution and determinants of
  health-related states or events in specified
  populations, and the application of this study to
  the control of health problems
• Last JM, ed. Dictionary of Epidemiology, Second
  edition. New York Oxford U. Press, 1988 42.
• Basic science of public health

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Risk factor

• Exposure associated with occurrence of disease
• Not necessarily causative

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Outbreak

• Occurrence of increased number of cases of a
  disease above the expected frequency

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Surveillance

• Monitoring diseases in population
• Passive reports submitted by practitioners,
  laboratories, hospitals
• Reportable diseases
• Active public health officials contact health
  care facilities for information

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Outbreak investigation

• 1. Establish existence of outbreak
• 2. Verify diagnosis
• 3. Develop case definition
• 4. Perform descriptive epidemiology
• 5. Analyze data

• 6. Develop hypothesis
• 7. Test hypothesis
• 8. Refine hypothesis
• 9. Implement control measures
• 10. Write report and disseminate findings

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Anthrax outbreak

• Fall 2001
• First case of bioterrorism in U.S.
• Investigation led by Centers for Disease Control
  (CDC)

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Anthrax

• Agent Bacillus anthracis
• Inhalational
• Cutaneous
• Gastrointestinal

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1. Establish existence of outbreak

• 22 cases of anthrax diagnosed October-November
  2001
• 11 cases of inhalational anthrax
• Last reported case of inhalational anthrax in
  U.S. was in 1976

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2. Verify diagnosis

• Clinical findings
• Skin lesions, fever, cough, chest pain
• Laboratory findings
• Isolation of B. anthracis from patient
• PCR of B. anthracis DNA
• Immunohistochemical staining
• Serology with ELISA

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3. Establish case definition

• Confirmed
• Clinical signs plus isolation or 2 supportive lab
  tests
• Suspected
• Clinical signs plus 1 supportive lab test or link
  to environmental exposure

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Search for more cases

• Search for more cases
• Hospital, clinic, medical examiners
• Staff at affected workplaces
• Reports from law enforcement and public
• Collect data
• Develop and administer questionnaire
• Cases and those potentially exposed
• Test clinical and environmental specimens
• 4 powder-containing envelopes recovered

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4. Perform descriptive epidemiology

• Who, what, where, when
• Plot epidemic curve
• Dates of onset of illness
• Plot spot map
• Locations of cases

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5. Analyze data

• Calculate frequency rates from descriptive
  epidemiology
• Age
• Sex
• Occupation
• Case-fatality ratio

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6. Develop hypothesis

• Why and how
• 2 separate mailings
• Exposures along path of mail and at delivery
  locations

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7. Test hypothesis

• Evaluate relationship between exposure and
  disease
• Compared cases between mailings
• Type of occupation
• Form of anthrax
• Cases persons with the disease
• Controls persons without the disease

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8. Refine hypothesis

• If original hypothesis failed
• May require further studies

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9. Implement control measures

• Treatment of cases
• Postexposure prophylaxis
• Inhalational case at workplace
• Environmental specimens at workplace
• 32,000 people received prophylaxis
• No further cases reported

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10. Write report and disseminate findings

• Numerous papers published on investigation

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Summary

• Multi-state investigation
• Involved local, state and federal agencies
• Thousands of people potentially affected

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References and acknowledgments

• Chin J. Control of communicable diseases manual.
  2000. American Public Health Assoc, Washington,
  DC. p 20.
• Dicker R. Principles of epidemiology self-study
  guide. Public Health Training Network. Atlanta
  Centers for Disease Control and Prevention.
  Available from www.phppo.cdc.gov/PHTN//catalog/30
  30g.asp
• Friis RH, Sellers TA. Epidemiology for public
  health practice. 1999. Aspen, Gaithersburg, MD.
  pp 52-53.
• Jernigan DB, Raghunathan PL, Bell BP, Brechner R,
  Bresnitz EA, Butler JC, et al. Investigation of
  bioterrorism-related anthrax, United States,
  2001 epidemiologic findings. Emerg Infect Dis
  serial online. 2002 Oct (cited 2005 Mar)8.
  Available from URL http//www.cdc.gov/ncidod/EID/
  vol8no10/02-0353.htm
• Slater MR. Veterinary epidemiology. 2003.
  Butterworth Heinemann, St. Louis, MO. p.
• Dr. Paul E. Grunenwald, Harris County Public
  Health and Environment Services