Evidence confirming the value of postexposure antiretroviral therapy in reducing the risk of occupationally acquired human immunodeficiency virus (HIV) infection has led to recommendations that prophylaxis be considered in persons with a recent sexual exposure to HIV. Katz and Gerberding discuss the use of antiretroviral prophylaxis after recent sexual exposure to HIV.

The authors note that no direct evidence points to prevention of HIV infection with antiretroviral therapy after sexual exposure, but they believe prevention is biologically plausible, given the similarities between the immune responses to transcutaneous and transmucosal exposures. They state that primary care physicians must be prepared to evaluate, treat and counsel patients with a recent sexual exposure to HIV. On the initial visit, the physician must (1) identify persons who may be candidates for postexposure prophylaxis and offer antiretroviral treatment, (2) perform HIV antibody testing to identify already existing infection and (3) intervene to prevent future transmission of HIV. Potential candidates for prophylaxis include persons who have engaged in unprotected anal or vaginal intercourse with a partner who is likely to be HIV infected, although the average risk may not apply to a specific encounter because of variation in source and host factors. HIV infection may result from a few contacts or may not occur despite many contacts.

Testing for HIV infection is appropriate but immediate initiation of prophylaxis should not be delayed. Patients found to be HIV positive at baseline should be prescribed an appropriate drug regimen for primary or longstanding HIV infection. If the partner is willing to be tested, this should be done. Antiretroviral prophylaxis can be stopped if the partner's test results are negative. If the partner is infected, viral load quantitation can help determine the likelihood of HIV transmission, which is increased in persons with advanced disease and higher viral loads.

Postexposure prophylaxis should be initiated within 72 hours of exposure. The treatment regimen should be modeled after the one used for occupational exposures. Some HIV experts recommend triple therapy for prophylaxis after sexual exposure, but the authors believe that a single drug may be adequate to counter the very small viral inoculum present immediately after sexual exposure. All patients with sexual exposure to HIV should be tested for other sexually transmitted diseases.

Counseling the patient about ways to reduce the risk of HIV exposure is appropriate. During follow-up visits, adverse reactions to drug therapy should be monitored, and HIV antibody testing should be repeated at six weeks, three months and six months. The symptoms of acute HIV seroconversion warrant prompt treatment.

The authors state that public health messages that emphasize the use of condoms and the avoidance of high-risk behaviors are the most effective ways of preventing HIV infection. Postexposure treatment is only a back-up method. However, the availability of postexposure prophylaxis may motivate patients to seek medical care, providing an opportunity to counsel and educate them about prevention.