Biomedical HIV prevention

John McAllister: St. Vincent's Hospital, Sydney


The most effective way to prevent the sexual transmission of human immunodeficiency virus (HIV) is to prevent HIV exposure. The consistent use of condoms is the mainstay of any personal, or population level, sexual risk reduction strategy. However, in an analysis of two large studies of condom use and HIV incidence in men who have sex with men, the overall effectiveness of condoms in preventing HV infection during anal sex was estimated at 70%.[1]  Ineffectiveness was related to condom failure e.g. breakage, slippage, leakage, and delayed and intermittent application during sex.[2]  Men who have sex with men represent the Australian population at most risk of HIV infection and while condom use should continue to be promoted, alone it is unlikely to reduce HIV incidence.

Antiretroviral drugs can be used to treat and prevent HIV infection. The final two decades of the 20th century saw not only the evolution of antiretroviral therapy (ART) used to effectively treat HIV infection but also the increased use of ART to prevent HIV acquisition in occupational, non-occupational, antenatal and postnatal settings. The first 15 years of the 21st century have advanced the use of ART as prevention in HIV-positive and -negative populations most notably in serodiscordant relationships and other groups of men and women at risk of HIV infection. Table 11 describes the various uses of ART as prevention. This section will focus primarily on HIV post-exposure prophylaxis (PEP) and HIV pre-exposure prophylaxis (PrEP) and describe the ways that a nurse might contribute to the assessment and care of HIV-negative men and women using ART.

Table 11: Antiretroviral therapy as prevention

Antiretroviral therapy as prevention




Postexposure prophylaxis



occupational PEP


non-occupational PEP

28 days of antiretroviral drugs taken as soon after, and within 72 hours of, an occupational or non-occupational (sexual or injecting drug use) actual or potential HIV exposure event

OPEP: 81% risk reduction[3]

NPEP: no empirical data, strongly supported by non-human primate and the prevention of mother-to-child HIV transmission studies[4] [5]

Prevention of mother-to-child HIV transmission


Universal antenatal HIV screening,

maternal ART, caesarean section,#short-course postnatal ART for the newborn and  avoidance of breast feeding

< 1% risk of vertical transmission (from a 13-40% risk without intervention)[6]

Treatment as prevention


ART to men or women with HIV infection in serodiscordant relationships

≥ 96%[7]

*Pre-exposure prophylaxis


Daily ART (usually coformulated tenofovir disoproxil fumarate and emtricitabine - Truvada) in HIV negative men and women

Men who have sex with men: 44 - 92%[8]

Heterosexual men and women: 75 - 90%[9]

IDU: 49 - 74%[10]

 ART: antiretroviral therapy; HIV: human immunodeficiency virus; IDU: injection drug user

# Additional benefit of caesarean section in women on antiretroviral therapy with an undetectable viral load is unknown
*Maximum efficiency is dependent on high levels of adherence and detectable drug in plasma. The range represents the overall efficacy and, in those participants with detectable drug, best efficacy. The study in injection drug users used tenofovir disoproxil fumarate alone.