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)
– ejaculation
– withdrawal

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 –
extremely low
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).