What is the HIV transmission risk/exposure?
All sexual risk estimations are for condomless sexual contact. It is assumed that a similar risk is incurred when a condom fails.
Table 1. Exposure and transmission risk/exposure with known HIV-positive source who is NOT on antiretroviral treatment.
See Literature Review1 section ‘Transmission risks associated with different exposures’ for further information.
|Type of exposure with known HIV-positive source who is NOT on antiretroviral treatment||Estimated risk of HIV
|Receptive anal intercourse (RAI)
|Shared needles and other injecting equipment||1/125|
|Insertive anal intercourse (IAI) uncircumcised||1/160|
|Insertive anal intercourse (IAI) circumcised||1/900|
|Receptive vaginal intercourse (RVI)||1/1250|
|Insertive vaginal intercourse (IVI)||1/2500|
|Receptive or insertive oral intercourse||Unable to estimate risk –
|Needlestick injury (NSI) or other sharps exposure||1/440|
|Mucous membrane and non-intact skin exposure†||< 1/1000|
* These estimates are based on prospective studies, not cross-sectional data or figures derived from modelling. These estimates do not take into account source viral load, which if undetectable markedly reduces risk estimates.
† Human bites are extremely low risk.
Many factors modify the risk of HIV transmission and should be considered in the risk assessment.
Viral load (VL):
- Higher plasma VL (when seroconverting or with advanced disease) is associated with increased risk of HIV transmission3
- Preliminary data shows no transmissions have occurred within male homosexual4 or heterosexual5 couples, from a partner with an undetectable VL.6
Undetectable viral load is defined in these guidelines as less than 50 copies/mL, consistent with the Seventh National HIV Strategy.7
Other factors that increase the risk of HIV transmission:
- a sexually transmissible infection (STI) in the source or exposed individual, especially genital ulcer disease and symptomatic gonococcal infections
- source ejaculation during receptive anal or vaginal intercourse
- a breach in genital mucosal integrity (e.g. trauma, genital piercing or genital tract infection)
- a breach in oral mucosal integrity when performing oral sex
- penetrating, percutaneous injuries with a hollow bore needle, direct intravenous or intra-arterial injection with a needle or syringe containing HIV-infected blood
- the uncircumcised status of the insertive HIV-negative partner practising insertive anal intercourse (IAI) or insertive vaginal intercourse (IVI).