US teenagers with HIV are reportedly taking more risks.

A new study reveals that teens are having more risky sex with more partners since the introduction of powerful HIV drugs.

The new treatment - highly active antiretroviral therapies, or HAART - was introduced in 1996, and has succeeded in lowering virus levels and prolonging the lives of thousands of HIV patients.

Researchers from UCLA writing in the American Journal of Health Behavior suggested that it was important to examine the effects of better treatment on promiscuity.

“Simultaneously, evidence suggests that many people living with HIV believe that sexual behaviours that could lead to the transmission of HIV, like unprotected sex, are less risky if viral levels are low,” said researcher Dr Marguerita Lightfoot.

The scientists compared the behaviour of 349 teens with HIV in Los Angeles, San Francisco, New York and Miami between 1994 and 1996, with 175 teens with HIV, and similar socio-economic characteristics, in the same cities between 1999 and 2000.

The 1999-2000 post-HAART group was almost twice as likely as the pre-HAART group to have had unprotected sex in the last three months. On average, post-HAART teens had nearly twice as many sexual partners as pre-HAART teens, while those in the later group were also more likely to have had a sexual partner who used injection drugs.

According to the US Center for Disease Control and Prevention, one quarter of the 40,000 new HIV infections in the US each year occur in people under age 21.

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