The risk for HIV infection among drug users is not the same between males and females, according to a new study. 

Researchers from Johns Hopkins University examined drug-related and sexual risk factors for HIV transmission in more than 1,800 drug users in Baltimore over a period of 10 years. All participants in the trial were at least 18 years old with a history of illegal injected drug use in the previous 10 years. Researchers gathered data on drug use and sexual activity during semi-annual interviews. Blood samples from participants were also retrieved at each visit. 

The study shows high-risk sexual behavior was the biggest predictor of HIV infection among intravenous drug users. Researchers found drug use and homosexual activity are the most important predictors of HIV infection among males, and high-risk heterosexual activity is the main predictor for HIV infection among females. Male drug users who reported homosexual activity were four times more likely to become infected with HIV, and in the female population, HIV infection was more than two times higher among women who reported having sex with another drug user than in women who used drugs but did not report any sexual activity with another drug user. 

Researchers say age is also an important determinant. They found drug users aged 30 and younger were more than twice as likely to develop HIV than those aged 40 and over. Steffanie Strathdee, M.D., from Johns Hopkins University, says, "This is consistent with several reports which indicate that younger intravenous drug users are more likely to engage in needle sharing and other behaviors that place them at higher risk of acquiring HIV and hepatitis B or C viruses."