This study, conducted at the Johns Hopkins University School of Public Health in Baltimore, Maryland, will determine how accurately injection drug users report their needle-sharing behavior. Needle-sharing is a major cause of blood-borne diseases, including HIV and hepatitis. Therefore, a better understanding of this behavior is critical for devising strategies to reduce disease spread in this way. Research on needle-sharing behavior has relied heavily on users' self-reports. This study will compare these self-reports with results of DNA tests that show whether a needle has been used by one or more individuals.

Injection drug users 18 years of age or older participating in the Baltimore Needle Exchange Program (BNEP) have been recruited for this study. Syringes distributed to users through the BNEP are collected after use and tested to differentiate between single versus multiple users. The findings are compared with the participants' responses about whether or not they shared their needles and syringes.

Participants visit the clinic every 6 months for an interview, including questions about their mental and physical health, drug use, sexual activity and knowledge about HIV (the virus that causes AIDS) and AIDS. After the interview, a small amount of blood is drawn for testing for HIV, hepatitis, syphilis and other infectious diseases. Some of the blood is stored for future testing. Participants return to the clinic 4 weeks after the interview and blood drawing to get their test results. At this time, they are offered referral for drug treatment, free condoms, advice about drug use and safer sex and an opportunity to ask questions about their health. Participation in the study may continue for up to 5 years.