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HIV Epidemiology


HIV Epidemiology

Contact Information
Los Angeles County
Department of Public Health
HIV Epidemiology, DHSP                       600 S. Commonwealth Ave. Suite 1920
Los Angeles, CA 90005
Phone: (213) 351-8196
Fax: (213) 487-9386


        LAC's ZIP code level data/maps on HIV

HIV Epidemiology - National HIV Behavioral Surveillance among Injecting Drug Users in Los Angeles County or "SHARPS”

Behavioral surveillance is defined as an "ongoing, systematic collection, analysis, and interpretation of behavior data for preventing or controlling disease or injury".1 According to CDC’s HIV/AIDS Strategic Plan objectives, behavioral surveillance is designed to reduce the proportion of persons at high risk for acquiring HIV and to increase the proportion of high-risk persons who routinely access voluntary counseling and testing or other HIV prevention services.

This behavioral surveillance system will provide relevant data on risk behaviors of persons who have injected illicit substances in the previous 12 months. Injecting drug users (IDUs) are a behavioral risk group composing 12% of all reported AIDS cases in Los Angeles County in 2002.2 IDU males who also have sex with men (MSM/IDU) contribute an additional 7% of the total newly diagnosed AIDS cases in 2002. Behavioral surveillance data can be used to evaluate whether prevention efforts are reaching IDUs and meeting local and national HIV prevention goals.3 Los Angeles County joins 24 other states and metropolitan areas in the National HIV Behavioral Surveillance (NHBS) system.


The purpose of the SHARPS project is to collect cross-sectional HIV risk data, once every three years, from adult men and women residing in Los Angeles County who have injected illicit substances in the previous 12 months. The study objectives are to: 1) assess the prevalence of and trends in drug-use and sexual risk behaviors; 2) assess the prevalence of and trends in HIV testing behaviors; and 3) assess the exposure to prevention messages and use of prevention services, impact of services, and gaps and missed opportunities for prevention.

Study Design:

Following an extensive formative research phase, the SHARPS team will implement respondent-driven sampling (RDS) to recruit a minimum sample of 500 IDUs in 2005 for the standardized behavioral surveillance questionnaire. Respondent-driven sampling (RDS) is a chain-referral strategy similar to snowball sampling. It is based on the recognition that peers are better able than outreach workers or researchers to locate and recruit other members of a hidden population. RDS starts with a limited number of “seeds” who are usually chosen by referral from key informants. Seeds are the starting point for the chain-referral sampling. These seeds complete a 30-minute interviewer-administered interview, and then are asked to recruit up to three members of their network who, for NHBS purposes, also inject drugs; the limited number of referrals helps reduce bias from any particular individual’s network size. Heckathorn 4-6 suggests that approximately 6 referral waves can produce a sample that resembles the underlying population of IDU within a geographic area in terms of major demographic characteristics (like race, age, gender). RDS provides a means of selecting a sample and also allows inferences about the characteristics of the population from which the sample is drawn

Contact Persons:

Ekow Kwa Sey, Study Epidemiologist, 213-351-8199

Trista Bingham, Principal Investigator, 213-351-8175

Report for download


  1. Tacker S, Berkelman R. Public health surveillance in the United States. Epidemiologic Reviews 1988; 10:164-190.
  2. HIV Epidemiology Program. An Epidemiologic Profile of HIV and AIDS in Los Angeles County, 2004. Los Angeles: Los Angeles County Department of Health Services; 2004.
  3. Mills S, Saidel T, Bennett A, et al. HIV risk behavioral surveillance: a methodology for monitoring behavioral trends. AIDS 1998;12 (suppl 2):S37-S46.
  4. Heckathorn D. Respondent-driven sampling: a new approach to the study of hidden population. Social Problems, 1997; 44(2):174-199.
  5. Heckathorn, D. Respondent-driven sampling II: Deriving valid population estimates from chain-referral samples of hidden populations. Social Problems, 2002; 49(1).
  6. Heckathorn D and Magnani R. Snowball and respondent-driven sampling. Draft book chapter to be published by Family Health International, 2004.

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