Epidemiology Applications Fran C. Wheeler, Ph.D School of Public Health University of South Carolina Columbia, SC (803)

Developed as part of an Enhanced AHEC Community Partnership for Health Professions Workforce and Educational Reform project funded by the Health Resource and Service Administration (HRSA)

OBJECTIVES l applications of epidemiologic method

Assessing Risk and Burden of Disease l Relative Risk l Odds Ratio l Attributable Risk

Relative Risk l Calculated to identify differences in disease rates between exposed and unexposed groups. l Risk of disease among exposed  risk of disease among unexposed s RR = 1, no difference s RR > 1, association between exposure and disease

Odds Ratio l Calculated to identify likelihood of exposure to a risk when comparing two groups, one with and one without disease. l Exposure odds in disease group  exposure odds in non-disease group s Ratio = 1, no association s Ratio > 1, association between exposure and disease

Attributable Risk l Calculated to identify the proportion of disease among exposed people that actually results from the exposure l Individual attributable risk = RR - 1 / RR l Population attributable risk = Pe (RR - 1) / 1 + Pe (RR - 1), where Pe = proportion of population exposed

Epidemiology in Action l Outbreak and Cluster Investigations l Public Health Surveillance l Community Screening Programs

Outbreaks and Clusters l Outbreak: an epidemic limited to a localized increase in the incidence of a disease l Cluster: an aggregation of relatively uncommon events or diseases in space and/or time in amounts believed or perceived to be greater than expected by chance

Characteristics of Outbreak Investigations l Infectious disease or condition l Etiologic agent is transmissible organism l Short time frame for investigation (hours, days) l Moderate to large effect estimates l Moderate to high exposure levels

Characteristics of Outbreak Investigations, cont. l Acute exposure period (hours, days) l Laboratory confirmation common l Moderate to high possibility of establishing cause and effect l Most common study design: retrospective cohort

Characteristics of Cluster Investigations l Non-infectious disease or condition l Often unknown or combined etiologic agents l Longer time frame for investigation (weeks or months) l Weak to moderate effect estimates l Low exposure levels

Characteristics of Cluster Investigations, cont. l Chronic exposure period (years or decades) l Laboratory confirmation uncommon l Low possibility of establishing cause and effect l Most common study design: case- control

Challenges of Cluster Investigations l Active or passive approach l Epidemiology or public health education l Data sources and denominators l Costs and yields

Public Health Surveillance l Ongoing systematic collection, analysis and interpretation of outcome-specific health data l Closely integrated with the timely dissemination of those data to those responsible for preventing and controlling disease or injury

Sources of Surveillance Data l Reports of health events l Reporting from laboratories l Registries l Vital statistics l Periodic surveys l Information on environmental exposures l Information from other organizations

Uses of Surveillance Information l Immediate detection l Annual dissemination l Archival information

Community Screening Programs l Defining the target population l Setting priorities among diseases and conditions l Choosing effective screening tests l Assessing the effectiveness of screening programs

Screening Tests

Hypothetical Example

Sample Data l AIDS l Syphilis l Diabetes

*Adjusted for reporting delays Quarter-Year of Diagnosis/Death N u m b e r o f C a s e s / D e a t h s Estimated Incidence of AIDS and Deaths of Adults with AIDS*, June 1998, United States 1993 definition implementation 25,000 20,000 15,000 10,000 5, AIDS Deaths

Female N=113,414 3 Age at Diagnosis AIDS Cases by Age and Sex Reported , United States ,000 10,000 15,000 20,000 25,000 30,000 35,000 Male N=574,783 Number of Cases

Estimated Number of Persons Living with AIDS , by Sex, United States Year Thousands Men Women

American Indian/ Alaska Native Black, not Hispanic Hispanic Asian/Pacific Islander White, not Hispanic Year Estimated Number of Persons Living with AIDS , by Race/Ethnicity, United States Thousands

Year ,500 2,000 1,500 1, American Indian/ Alaska Native Asian/Pacific Islander Estimated Number of Persons Living with AIDS , by Race/Ethnicity, United States Persons

U.S. dependencies and possessions Midwest Northeast South Year Estimated Number of Persons Living with AIDS , by Region, United States West Thousands

Year of Report American Indian/ Alaska Native Black, not Hispanic Hispanic Asian/Pacific Islander White, not Hispanic Proportion of AIDS Cases, by Race/Ethnicity Year of Report, , United States Percent of Cases

Excludes cases with other or unreported risk pending medical record review and reclassification Year of Report AIDS Cases by Exposure Category and Year of Report, , United States MSM & IDU Men who have sex with men (MSM) Injection drug use (IDU) Heterosexual contact Percent of Cases

VI 29.6 PR 44.3 < AIDS Rates per 100,000 Population Reported in1998 Rate per 100,000 DE MA RI CT NJ MD DC NH VT 3.4

71% 12% 13% AIDS Cases N=48,269* Population N=274,766,000 AIDS Cases Reported in 1998 and Estimated 1998 Population, by Race/Ethnicity, United States White, not Hispanic Black, not Hispanic Hispanic Asian/Pacific Islander American Indian/ Alaska Native 33% 45% 20% *Includes 211 persons with unknown race/ethnicity <1% 1%1% 1%1% 4%4%

AIDS in Adult/Adolescent Men by Race/Ethnicity per 100,000 Population, Reported in 1998 United States Race/Ethnicity White, not Hispanic Black, not Hispanic Hispanic Asian/Pacific Islander American Indian/ Alaska Native Total* * Includes 162 men whose race/ethnicity is unknown. Cases 14,027 14,740 7, ,886 Rate

Northeast N=14,399 North Central N=4,317 South N=19,474 West N=8,121 Metropolitan area 50, ,999 population Non- metropolitan area AIDS by Region & Size of Place of Residence Reported in 1998, United States % % Metropolitan area 500,000 population