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Post-Exposure Prevention

April 2000

There has been growing interest in the use of Post-Exposure Prevention (PEP) as a means of preventing HIV infection. PEP involves a person beginning anti-HIV therapy within hours of suspected HIV exposure, with a goal of blocking the establishment of HIV infection.

Certainly the use of anti-HIV therapy by HIV-positive pregnant women and their newborns has been extremely effective in lowering the rate of mother-to-child HIV transmission. The use of anti-HIV therapy among HIV-negative healthcare workers, within hours of a possible HIV exposure (e.g. needle-stick accident with a needle exposed to HIV-infected blood), is standard of care in hospital and clinic settings and has been shown to reduce the risk of developing HIV infection. There is a great deal of controversy, however, about the risks, benefits and public health impact of using PEP among HIV-negative people who have had a recent possible sexual or injection drug use-related HIV exposure. Three posters presented at the recent Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) provided additional insight into the use of PEP for sexual and other non-occupational exposures.

France, Switzerland and Australia are the only countries in the world with recommendations and guidelines for the use of PEP for suspected sexual HIV exposure. A small observational study in Lyon, France evaluated PEP use and follow up in sexual assault victims. To be eligible for PEP, a person must arrive at the clinic and start anti-HIV therapy within 48 hours of the possible HIV exposure incident. Anti-HIV therapy is continued for four weeks with intensive monitoring.

While no data were available regarding HIV transmission rates, interesting information was provided regarding the use of PEP in this setting. Of the 65 people seen at the Lyon clinic, nine were ineligible for PEP because they arrived more than 48 hours after the potential HIV exposure. Thirty-five people, slightly more than half, chose to start PEP, but of those, only 19 returned to the clinic for follow-up visits. Findings from the French study suggest that programs to enhance follow-up for PEP recipients are critical, not only to document the effectiveness of PEP but also to monitor for side effects of anti-HIV therapies.

In Brazil, a study of PEP nested within a larger study looking at new infection rates among gay men evaluated the impact of PEP usage on subsequent HIV risk-taking behaviors. While the primary study is quite large (202 gay men), the PEP study included only 29 men who presented within 48 hours of a suspected HIV exposure and elected to use anti-HIV therapy. In the overall study, after 18 months of follow up, three people have become HIV positive, none of whom received PEP. None of the 29 men who received PEP has become HIV positive.

The individuals who chose PEP had documented repeated high-risk behavior (e.g. unprotected sex) which persisted over time. The decision to use PEP neither increased nor decreased their risk-taking activities. Of the 29 people who chose PEP, a few individuals repeated the use of PEP because of subsequent suspected HIV exposures. Three people initiated PEP twice and one person initiated four courses of PEP over the 18 months follow up of the study.

The largest study of PEP was reported by Dr. Michelle Roland of UCSF. This study enrolled 436 people who initiated PEP within 72 hours of a suspected non-occupational HIV exposure. In this study PEP included HIV testing, ongoing risk reduction and adherence counseling, the option to use one month of anti-HIV therapy and intensive monitoring. Not all individuals chose to use anti-HIV therapy, but all individuals, regardless of their decision about anti-HIV therapy, were encouraged to remain in the PEP program for counseling and monitoring. The majority of individuals who chose to receive anti-HIV therapy received dual nucleoside analogue reverse transcriptase inhibitor (NARTI) therapy.

Six month follow up data are available on 293 people and twelve-month follow up information is available on 145 people. Thus far, four people in the study have become HIV positive. This includes one person who did not choose to take anti-HIV therapy and three people who initiated anti-HIV therapy. None of the four infections are believed to be associated with the suspected HIV exposure incident that first brought the individual to the clinic. All four people reported repeated high-risk activities after their initial intake into the PEP program.

Of note, one of the women in the study who became HIV-positive engaged only in protected sex with her HIV-positive partner after presenting to the study as a result of a broken condom. Six months after her course of anti-HIV PEP therapy, she and her partner began having unprotected sex when his HIV levels fell below the limit of detection, believing he was not infectious. Shortly thereafter she developed symptoms of an acute infection syndrome and later documented HIV infection. This particular case underscores the need for continued safe sex practices among people living with HIV who have optimally suppressed HIV levels to below the limit of detection of current tests. Having undetectable HIV levels in the blood does not mean that HIV is absent in either semen or vaginal secretions, nor does it mean a person cannot transmit HIV. Some existing data also suggests that it takes longer to reach "undetectable" levels of HIV in semen or genital secretions than it does in the blood. Thus, reaching undetectable levels in the blood -- the only thing that most patients can easily measure -- should never be considered a sign that a person has suddenly become incapable of transmitting virus to others.


Commentary

None of the above studies either confirms or denies the value of anti-HIV therapy in preventing HIV infection in the non-occupational HIV exposure setting. The use of PEP for sexual, injection drug use or other non-occupational exposures is extremely controversial. While in the setting of occupational (healthcare worker) HIV exposure, the use of anti-HIV therapy within a few hours of suspected HIV exposure has been shown to decrease HIV transmission/infection rates, it is not clear that this finding applies in any other setting. It is unknown if starting therapy after 24-36 hours will have any impact on blocking an HIV infection when exposure to HIV has occurred. Moreover, the majority of people with a suspected exposure to HIV, regardless of the use of therapy, will not go on to develop an established HIV infection.

For people who repeatedly engage in high-risk activities that may result in an exposure to HIV, the repeated use of anti-HIV therapy could theoretically weaken the immune system and leave them more susceptible to HIV infection. This is not to say that anti-HIV therapy weakens the immune system, per se, but rather that the drugs do have side effects and they can be hard on the body, as any person taking the drugs to treat HIV can well testify. In general, the use of PEP is not recommended for people who document repeated high-risk HIV exposure activities.

The most effective way to prevent HIV infection is to reduce risk-taking behavior, practice safer sex, use clean works and don't share needles or works. Project Inform is developing a discussion paper on PEP that should be completed by the end of this year. For a full discussion of issues regarding PEP for non-occupational HIV exposure, call Project Inform's Hotline or check the website to see if the paper is available. For more information on preventing mother-to-child HIV transmission, ask for the new discussion paper on this topic. However, as a general rule, the Project Inform hotline is not a prevention counseling hotline. If you have specific questions about HIV prevention, risk behavior or risk reduction counseling call the Centers for Disease Control's National HIV/AIDS Prevention Hotline at 1-800-458-5231.


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