Risks when the index’s HIV status is unknown

National guidelines tell us the chance of people having HIV with a detectable viral load. Some people have a higher chance than others for example men who have sex with men, people who have come to live in the UK from countries where HIV is a lot more common (particularly sub Saharan Africa) and some people who inject drugs.

For example a man who has sex with men in England is thought to have around a 1 in 43 chance of having HIV with a detectable viral load. For heterosexual men and women in the UK who are not of Black African ethnicity the chance is about 1 in 5,000 and 1 in 10,000. For heterosexual men and women in the UK who are Black African ethnicity the chance is about 1 in 172 and 1 in 114.

If it is not known if the index has HIV but is either

from a country of high prevalence particularly sub Saharan Africa - country specific HIV prevalence can be found within the UNAIDS epidemic and response data
a man who has sex with men
a person who injects drugs from high risk countries particularly Eastern Europe and Central Asia – HIV prevalence within people who inject drugs is available from the UNAIDS key populations data.

and

if the patient received anal sex without a condom (or the condom burst/came off) PEP is normally recommended
If the patient gave (insertive) anal sex or received vaginal sex without a condom (or the condom burst/came off) then the following factors should be taken into account:
- breaches in the mucosal barrier such as genital ulcer disease or trauma following sexual assault or first intercourse
- multiple episodes of exposure within a short period of time eg group sex
- sexually transmitted infection in either partner
- more detailed knowledge of local HIV prevalence within the index case population

PEP may then be considered for insertive anal sex but is generally not recommended and is likely to be rarely given for receptive vaginal sex unless there are clear specific extenuating factors which increase the risk.

PEP is not recommended when the exposure is insertive vaginal sex

Proactive attempts should be made to establish the HIV status of the index partner whilst not delaying PEP.