Epidemiologic Surveillance and Outbreak Investigation Presented by CPT Kathy Hughes DVM, TXSG Houston Med Response Group Texas Medical Rangers 23 Mar 05

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

Risk factor Exposure associated with occurrence of disease Not necessarily causative

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

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

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

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

Anthrax Agent: Bacillus anthracis Inhalational Cutaneous Gastrointestinal

1. Establish existence of outbreak 22 cases of anthrax diagnosed October- November cases of inhalational anthrax Last reported case of inhalational anthrax in U.S. was in 1976

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

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

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

4. Perform descriptive epidemiology Who, what, where, when Plot epidemic curve Dates of onset of illness Plot spot map Locations of cases

5. Analyze data Calculate frequency rates from descriptive epidemiology Age Sex Occupation Case-fatality ratio

Table 2. Comparison of inhalational and cutaneous bioterrorism-related anthrax cases, United States, 2001 Case characteristic All cases, n=2 2 (%) Inhalational cases n=11, (%) Cutaneous cases n=11, (%) p value (inhal. vs. cutan.) Median age (range), years a 46 (0.6–94)56 (43–94)35 (0.6–51)<0.01 Male sex 12 (55)7 (64)5 (45)0.7 Occupation/exposure site a Mail handler 12 (55)8 (73)4 (36)0.13 Media company employees 6 (27)1 (9)5 (45) Other 4 (18)2 (18) No./deaths (case-fatality ratio) 5 (23)5 (45)0 (0)0.04 No. of cases following contaminated letters b September 18 mailing 11 (50)2 (18)9 (81)<0.01 October 9 mailing 8 (36)7 (64)1 (9) a Associations suggest that age and occupation varied between inhalational and cutaneous cases; however, it is uncertain if age or occupation were significant independent factors for having a case of anthrax. Wilcoxon two-sample test for nonparametric data was used. All other measurements used two-sided Fisher’s exact test. b Based on documented or presumed paths of contaminated envelopes; excludes three case-patients who could not be linked to a particular mailing.

6. Develop hypothesis Why and how 2 separate mailings Exposures along path of mail and at delivery locations

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

Table 2. Comparison of inhalational and cutaneous bioterrorism-related anthrax cases, United States, 2001 Case characteristic All cases, n=2 2 (%) Inhalational cases n=11, (%) Cutaneous cases n=11, (%) p value (inhal. vs. cutan.) Median age (range), years a 46 (0.6–94)56 (43–94)35 (0.6–51)<0.01 Male sex 12 (55)7 (64)5 (45)0.7 Occupation/exposure site a Mail handler 12 (55)8 (73)4 (36)0.13 Media company employees 6 (27)1 (9)5 (45) Other 4 (18)2 (18) No./deaths (case-fatality ratio) 5 (23)5 (45)0 (0)0.04 No. of cases following contaminated letters b September 18 mailing 11 (50)2 (18)9 (81)<0.01 October 9 mailing 8 (36)7 (64)1 (9) a Associations suggest that age and occupation varied between inhalational and cutaneous cases; however, it is uncertain if age or occupation were significant independent factors for having a case of anthrax. Wilcoxon two-sample test for nonparametric data was used. All other measurements used two-sided Fisher’s exact test. b Based on documented or presumed paths of contaminated envelopes; excludes three case-patients who could not be linked to a particular mailing.

8. Refine hypothesis If original hypothesis failed May require further studies

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

10. Write report and disseminate findings Numerous papers published on investigation

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

References and acknowledgments Chin J. Control of communicable diseases manual 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: Friis RH, Sellers TA. Epidemiology for public health practice Aspen, Gaithersburg, MD. pp 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] Oct (cited 2005 Mar);8. Available from URL: Slater MR. Veterinary epidemiology Butterworth Heinemann, St. Louis, MO. p. Dr. Paul E. Grunenwald, Harris County Public Health and Environment Services