Question:

I am a recent victim of sexual assault, namely anonymous rape. I was blacked out and I have no idea if the assailant was wearing a condom or not. I have taken all necessary steps i.e. urgent care, rape kits and police notification and it did not appear that the rapist ejaculated inside of me. I am still very concerned about the retrovirus - HIV. How long does it take to be determined as HIV positive? I am under the impression that one can have a sexual encounter and not be diagnosed for quite awhile after the incident. Is this due to a undetectable viral load? Thank you.

Answer provided by:

Rodger MacArthur, M.D.
Wayne State University
Division of Infectious Diseases

The best information on the time course of infection with HIV following exposure comes from studies looking at the acute retroviral syndrome. The acute retroviral syndrome is a constellation of non-specific signs and symptoms (e.g., high fever, adenopathy, pharyngitis) that occur in about 1/3 of persons exposed to HIV who ultimately seroconvert from HIV-negative to HIV-positive. On average, it takes 2-4 weeks for signs and symptoms of the acute retroviral syndrome to appear following an exposure to HIV; well-documented instances of the acute retroviral syndrome have occurred in which the exposure was 1-6 weeks earlier. At the time that the symptoms appear, the HIV RNA level (viral load) in the exposed individual is very high, but antibody to HIV (“HIV test”) is not detectable or only weakly detectable. It typically takes an additional 3-6 weeks following the onset of signs and symptoms for the HIV antibody test to become definitively positive.

In other words, on average, it is estimated that it takes 4-8 weeks following exposure to HIV to become HIV antibody-positive. The Centers for Disease Control (CDC) estimates that over 95% of persons who ultimately turn HIV-positive will do so within 3 months following an exposure, and that essentially everyone who ultimately seroconverts will do so within 6 months of exposure. The CDC recommends testing following an exposure at baseline, 4-6 weeks following exposure, and at 3 and 6 months following exposure.

The use of antiretroviral therapy to decrease the chances of seroconversion in the exposed individual following a sexual exposure to HIV is controversial. It is estimated that post-exposure prophylaxis, when initiated in the hospital setting (non-sexual exposure) within a few hours of exposure, and continued for 4 weeks, can reduce the likelihood of seroconversion by 80%. There are many reasons why post-exposure prophylaxis has not become standard of care following a sexual exposure, including 1) typical delays in reporting the exposure of more than a few hours; 2) difficulty in quantifying risk of seroconversion following a sexual exposure; and 3) lack of data on efficacy of post-exposure prophylaxis following a sexual exposure. Nevertheless, many authorities recommend that serious consideration be given to the use of antiretroviral therapy following a sexual exposure, especially in cases of rape reported within a few hours. It is not clear from the question if the issue of post-exposure prophylaxis was discussed, although the risk of HIV seroconversion in this case seems low (no semen detected; assailant not known to be definitely HIV-positive).

In summary, the risk of seroconversion to HIV-positive in this case seems low. Repeated HIV antibody testing should be performed out to 6 months, even though most individuals who ultimately seroconvert will do so within the first 4-8 weeks following an exposure to HIV.

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