Failures following HIV post-exposure prevention provide valuable lessons for warding off future infections

September 27, 1999

Patients enrolled in the San Francisco Post-Exposure Preventive (PEP) Project became infected with HIV more than six months after their initial exposure to the virus because of subsequent and ongoing contact with HIV-infected partners. Four case studies will be presented at the Interscience Conference on Anti-Microbial Agents and Chemotherapy on September 26 in San Francisco.

"Clinicians and prevention programs need to help people understand the increased risk of becoming infected through repeated exposures to HIV," said Michelle Roland, MD, assistant professor of medicine, UCSF Positive Health Program at San Francisco General Hospital Medical Center and lead author of the study. "The most important thing we can do is help people identify barriers to protecting themselves and offer resources to overcome those barriers."

The PEP project, jointly run by the UC San Francisco AIDS Research Institute and the San Francisco Department of Public Health, offers comprehensive treatment to high-risk sexually active people and injection drug users who may have been exposed to HIV. Treatment includes HIV testing, risk-reduction counseling, and anti-viral drug intervention.

The project enrolled 436 persons exposed to HIV and provided services for almost 500 HIV exposures between October, 1997 and April, 1999. After four weeks of counseling and anti-retroviral therapy, none of the exposed individuals became infected. However, four patients have subsequently become infected at least six months after their initial exposure to the virus. Three experienced seroconversion, the point at which HIV antibodies reach a detectable level in the blood and HIV infection is confirmed. A fourth person showed symptoms of acute HIV infection, a condition where the virus can be seen in the plasma but antibodies are yet to be produced.

"We identified two barriers that clinicians and prevention programs should address based on the four case histories," said Roland. "First, counseling strategies should target common misconceptions about transmission among both HIV positive and HIV negative people. And, second, it is important to provide risk-reduction counseling and referrals in conjunction with anti-viral drug regimes."

Misconceptions can result in unsafe sexual practices, said Roland. For example, many people believe it is safe to have unprotected sex with a partner whose plasma viral load is undetectable. The amount of virus in genital secretions, however, is often unrelated to the amount of virus in plasma, said Roland. In one case study, a woman engaged in protected sex after a possible exposure to HIV and tested negative six months after PEP enrollment. However, when her partner's plasma viral load became undetectable they decided to have unprotected sex, and the woman became infected.

The other cases highlight the importance of reducing HIV exposures and the need for ongoing counseling, said Roland. In all three instances, people continued to engage in unprotected sex with known HIV positive partners and/or use injection drugs despite participation in the PEP program. In one case, a standard anti-body test (LS-EIA) suggested infection occurred months after taking PEP medications.

"It is important to remember that our study was not testing the effectiveness of anti-viral medications," said Roland. "They may work, but taking medication without an increase in safer sex and injection drug use practices can result in HIV infections."

The researchers will continue to follow people enrolled in the PEP project through April, 2000 and hope to conduct further studies on effective and feasible counseling strategies in conjunction with anti-viral medications, to help keep HV negative individuals healthy and uninfected said Roland.

In addition to Roland, co-presenters include Jeffrey Martin, M.D., Center for AIDS Prevention Studies; Joshua Bamberger, M.D., San Francisco Department of Public Health; Mitchell Katz, M.D., Department of Public Health; Thomas Coates, Ph.D., director of the UCSF AIDS Research Institute, and James Kahn, M.D., associate professor in the UCSF Positive Health Program at San Francisco General Hospital Medical Center.

University of California - San Francisco

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