The risk of HIV transmission through a single exposure is determined by:
- The nature of the exposure with its estimated risk per exposure (Table 1)
- If the source is known to be HIV positive and viraemic (Table 2)
- The risk that the source is HIV positive and viraemic if their status is unknown (Table 2 and Appendix A)
- Additional factors which likely or potentially increase the risk of HIV transmission (outlined in footnotes of Table 2)
Table 1. Estimated risk of HIV transmission by exposure22,36-44
| Exposure | Risk |
|---|---|
Receptive anal intercourse (RAI)
| 1:70 1:155 |
| Insertive anal intercourse (IAI) – index uncircumcised – index circumcised | 1:160 1:900 |
| Receptive vaginal intercourse (RVI) | 1:1250 |
| Insertive vaginal intercourse (IVI) | 1:2500 |
| Fellatio | Negligible |
| Cunnilingus | Negligible |
| Mucous membrane/non-intact skin | 1:1000 |
| Intact skin exposure | Negligible |
| Human bite | Negligible |
| Shared injecting equipment | 1:125 |
| Occupational needle stick injury | 1:440 |
| Community needle stick from a discarded needle | Negligible* |
| Blood transfusion | 1:1 |
* Worldwide, there have been no reported cases of HIV acquisition from a discarded needle in a public place.45 Very rare transmission of HBV and HCV have occurred in this situation, so these infections need to be considered.
Note: These figures are estimates derived from cohort and modelling studies, where HIV status, treatment status and HIV viral load of source or sexual partners were either self-reported or unknown. All sexual risk estimations are for condomless sexual contact. It is assumed that a similar risk is incurred when a condom fails.
