Background
Although the most effective method of preventing HIV infection is avoidance of exposure, questions arise as to the effectiveness of and strategy for antiviral prophylaxis following nonoccupational exposure. The CDC recently released guidelines for this complex clinical presentation.
Conclusions
There are nearly 40,000 new HIV infections annually in the United States. At this time, few individuals seek care after nonoccupational exposure. In addition, some patients are not appropriate candidates for nonoccupational postexposure HIV prophylaxis (nPEP) because of recurring high-risk exposures.
Surveys indicate that 69% of HIV-discordant couples report unprotected intercourse in the previous 6 months, and 17% of bisexual or homosexual men report condom failure in the last 6 months.
In a national sample, 13% of women reported having been raped, and 60% of these rapes occurred before age 18. Male victims account for nearly 12% of reported rapes in the United States.
In animal studies, tenofovir blocked intravenous transmission of simian immunodeficiency virus if given within 24 hours of exposure and continued for 28 days. Delay until 48-72 hours and shorter duration of therapy diminished effectiveness.
In humans, it is estimated that prompt initiation of zidovudine after a needle stick reduces the risk of HIV transmission by 81%. Clinical trials indicate that single-dose therapy to laboring HIV-infected mothers coupled with a dose of antiviral agents to the neonate within 72 hours of birth substantially reduces peripartum transmission of the virus.
Studies of the cost effectiveness of nPEP endorse therapy only for patients exposed to a known source of HIV and those who have had repeated receptive anal intercourse with a homosexual or bisexual partner of unknown serostatus.
Implementation
▸ When counseling a patient post exposure, the following rates of transmission per 10,000 events may be of value: 9,000 infections after infected blood transfusion, 67 infections after sharing needles, 50 infections after receptive anal intercourse, 30 infections after a needle stick, 10 infections after receptive vaginal intercourse, 5-7 infections after insertive intercourse, and 0.5-1 infections after oral intercourse.
▸ Risk for transmission might be greatest if the source had been infected recently, which is associated with high viral loads in body fluids.
▸ The following signs and symptoms are present in acute retroviral infections: 96% of patients have fever, 74% have lymphadenopathy, 70% have pharyngitis, 70% have rash, 54% have myalgias/arthralgias, 33% have diarrhea or headache, and 27% have nausea and vomiting.
▸ In assessing a patient with high-risk behavior for nPEP, a physician should consider the patient's ongoing risk-reduction behavior in the context of the recent exposure. These patients should be offered counseling to help them change their lifestyles and thereby reduce the continued risk of infection.
▸ The CDC recommends prompt (within 72 hours) initiation of highly active antiretroviral therapy (HAART) and continuation for 28 days in patients with exposure to sources known to be HIV infected or when the event poses substantial risk for transmission. Patients with small exposure risks or those who are seen more than 72 hours after the event should not receive nPEP. Other circumstances warrant careful assessment of the benefits versus the risks of initiating therapy.
▸ Current data indicate that nPEP is less likely to be effective if started more than 72 hours after exposure. After such delays, the potential benefit may not outweigh the risks of taking antiviral medication.
▸ There are two preferred regimens. One is efavirenz and either lamivudine or emtricitabine with either zidovudine or tenofovir. The other is lopinavir/ritonavir (Kaletra) and zidovudine plus either lamivudine or emtricitabine.
▸ Prior to initiation of nPEP, patients should themselves be screened for HIV to avoid treatment of a patient with more remote infection.
▸ Frequent side effects of postexposure prophylaxis include nausea (57%) and fatigue or malaise (38%). Nevirapine has been associated with severe hepatotoxicity as well as pronounced skin reactions; it should not be used for postexposure prophylaxis.
▸ Patients seeking care after a potential exposure to HIV should be serotested at baseline, 3 months, and 6 months after the critical event. There have been reports of low viral load levels (fewer than 3,000 copies) after exposure in patients who do not subsequently seroconvert.
▸ Patients who seroconvert despite the use of combination antiretroviral therapy should be tested for resistance to guide ongoing therapy.
▸ In several studies it was found that most victims of sexual assault refuse or do not complete the 28-day course of antiviral prophylaxis. They should be offered supportive counseling, appropriate testing, prophylaxis for STDs, and emergency contraception.