Etiology
HIV can be transmitted via blood and other body fluids. Certain types of exposure to HIV are more risky, and, following these risky episodes, post-exposure prophylaxis (PEP) should be considered.
The decision to prescribe PEP is based on the risk of HIV transmission to the HIV-negative person.
The estimated risk of HIV transmission following an exposure from a known person with HIV not on suppressive antiretroviral therapy is as follows, in order from highest to lowest risk:[14][15][16][17][18][19][20][21][22][23][24]
90% to 100%: blood transfusion (1 unit)
0.67%: sharing injecting equipment
0.3%: needlestick injury
0.1% to 3.0%: receptive anal intercourse
0.1% to 0.2%: receptive vaginal intercourse
0.09%: mucus membrane exposure
0.06%: insertive anal intercourse
0.03% to 0.09%: insertive vaginal intercourse
0% to 0.04%: receptive oral sex (fellatio).
Risk of HIV transmission depends on multiple factors, including HIV status of the source (or prevalence of HIV viremia in the source group, if source HIV status is unknown), characteristics of the source such as HIV viral load, and, in the case of sexual exposures, coinfections with other sexually transmitted infections, especially genital ulcer disease.[25] If the exposure recipient has active genital ulcer disease this can also increase the likelihood of HIV transmission via sexual exposure from the source. Other factors associated with an increased risk of HIV transmission include menstruation or other bleeding, and pregnancy or postpartum.[3] Increased risk of occupationally acquired HIV infection includes deep injury, visible blood on device, exposure to a device used in the source's artery or vein, and high viral load in the source patient.[26]
Pathophysiology
Following exposure to the HIV virus, there is a small window of opportunity from when inoculation occurs to when the virus can be detected in the regional lymph nodes and then in the bloodstream.[1][2] The basis for the recommended time to initiation of post-exposure prophylaxis (PEP) comes from evidence that shows it may take 48 to 72 hours for the virus to enter the regional lymph nodes.[2]
Animal studies demonstrate that PEP is effective in monkeys if given early and for a full 28 days.[27][28]
There have not been any randomized controlled trials of PEP in humans due to ethical concerns. Data have been gathered from animal studies, prevention of mother-to-child transmission programs, healthcare workers who have been exposed to HIV, sexual assault victims, and from men who had sex with men in Brazil who were given PEP to take immediately after sexual exposure.[26][29][30] These studies have been used as the rationale for prescribing PEP in both the occupational and nonoccupational settings.
Classification
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