THE VOICE OF CHICAGO'S GAY, LESBIAN, BI, TRANS AND QUEER COMMUNITY SINCE 1985

Researchers have long known that HIV viral load is a reverse J curve—initially very high, often in the millions of copies of the virus; then generally dropping to a plateau of several hundred or several thousand copies as the immune system offers some suppression; finally rising again in the final stage of the disease as the immune system is overwhelmed.

Viral load is one of the most important factors in whether or not a virus is transmitted to an exposed person. Researchers have created models suggesting that about half of all new HIV transmissions are passed on during the first three months of infection.

That is before most people would even know they were infected because the test most commonly used to screen for HIV would not detect antibodies to the virus.

The first data confirming that modeling has come from an ongoing survey of thousands of villagers in the Rakai district of southern Uganda. It is published in the May 1 edition of the Journal of Infectious Disease.

Columbia University researcher Maria J. Wawer and colleagues examined survey data and blood samples taken between 1994 and 1999 to identify 235 monogamous couples where one or both became infected with HIV through vaginal sex during that period. Treatment for HIV was not available in Uganda at the time.

Nearly half of the new infections could be attributed to a partner who themselves had become infected within a two and a half month window immediately prior to passing on the virus. That was about five and a half times the rate of transmission at the trough of established infection, the period six or more months after infection when the immune system is helping to suppress the virus.

Even at the end stage of disease, when patients were dying and viral load was increasing, the rate of transmission was only double that of the trough period.

Because of the way the study was conducted, Wawer said the rate of new transmission of HIV during vaginal sex could be as high as 1 in 50 during the first month of post-infection.

Transmission of HIV through unprotected receptive anal sex is several-fold more efficient than through vaginal sex because the rectum is a much more fragile tissue that is designed to absorb water and nutrients. That could drop the odds of becoming infected through anal sex with an acutely infected partner to about a fifty-fifty shot at each encounter.

A person with an established HIV infection, particularly one who is on an effective therapy, offers reduced risk of passing on the virus. The irony is that the person who tests negative for HIV could be the one that puts you most at risk for becoming infected. It points out the need to play smart when it comes to sex.