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Low HIV levels may reduce risk of spreading the virus

An encouraging study suggests that people with very low levels of the AIDS virus in their blood are unlikely to spread HIV to others.

The study, conducted in Africa, could have important implications for the future of the AIDS epidemic in the United States, where drug treatment has lowered virus levels for many.

However, for several reasons, the conditions studied in Africa do not precisely mirror the U.S. AIDS situation, and experts caution that the research should not lull Americans into giving up safe sex practices. Unprotected sex with an HIV-infected person always carries risk, no matter how low their virus level.

The study looked at sexual transmission of HIV in rural Uganda. It was conducted by Dr. Thomas C. Quinn and others from Johns Hopkins University and presented Sunday at the 7th Conference on Retroviruses and Opportunistic Infections.

The doctors followed 415 heterosexual couples in which one partner was infected with HIV and one was not. Despite receiving free condoms, the couples rarely used them. During 30 months of follow-up, 90 people in the study caught the virus.

The study found that the higher the level of HIV in the infected person's blood, the higher the risk of passing on the virus through sex.

Doctors measure the number of individual viruses in a milliliter of blood. The study found that someone with 200,000 copies of virus is 2{ times more likely to spread HIV than is someone with 2,000 copies.

However, the researchers found no transmission of virus by infected people who carried less than 1,500 copies of the virus, even though they had sex without condoms.

Because of the high expense, AIDS treatment is rare in Africa. However, in the United States, doctors typically try to reduce patients' virus levels to below the level of detection, which is about 50 copies per milliliter.

About half of all U.S. patients fail to reach this undetectable level consistently.

"It's wonderful news, and there is a lot we can learn from it," Dr. Helene Gayle, AIDS chief at the U.S. Centers for Disease Control and Prevention, said of the study.

However, both she and Quinn cautioned that the situation is not identical in the United States. They noted that in Africa, people may have low virus levels because their immune systems are still strong enough to fight HIV.

But in the United States, many people's virus levels are lowered by treatment with AIDS medicines.

Doctors say it is theoretically possible that people with drug-suppressed HIV carry more virus in their semen and vaginal secretions than do those with naturally low levels. If so, this could make their risk of transmission greater.

The African study looked only at heterosexual transmission. Doctors note that HIV spreads much more readily through anal sex than through heterosexual intercourse. So unprotected sex at very low virus levels may be riskier for homosexuals.