Estimated Exposure Risks

MEN WHO HAVE SEX WITH MEN (MSM)

When working out the patient's risk factors there are many pertinent questions to be asked. It is important to remember that MSM remain the group at greatest risk of acquiring HIV infection within the UK, accounting for an estimated 84 per cent of infections diagnosed in 2003 (data: HPA). The impact of HIV on MSM in the UK has been profound: 31,430 MSM have been reported as HIV-positive, of whom 12,460 have progressed to AIDS; of these, 9,693 died. Improved survival since the advent of effective antiretroviral therapy in the past decade, with sustained numbers of new HIV diagnoses, has led to increasing numbers of MSM living with diagnosed HIV infection. In the UK it was estimated that, at the end of 2003, just under half (46 per cent, 24,500/53,000) of all HIV infections among adults were among MSM. Furthermore, 26 per cent (6,400) of MSM were unaware of their infection, accounting for 45 per cent of the estimated 14,300 undiagnosed prevalent infections. Data from the Enhanced Syphilis Surveillance programme, collected between April 2001 and September 2004, indicate that 53 per cent (558/1,048) of MSM diagnosed with syphilis in London were known to have co-infection with HIV.

BLACK AND OTHER MINORITY ETHNIC GROUPS

The UK's black and ethnic minority populations continue to be disproportionately affected by poor sexual health.The groups affected and their experiences of HIV and STIs vary greatly, reflecting the diversity present in the migratory patterns, socio-economic circumstances, and experiences of disadvantage and discrimination in these populations. Variation in the incidence of STIs among black and ethnic minority groups is further influenced by several factors, including diverse sexual attitudes and behaviours, patterns of sexual mixing, and differential access to sexual health services. Both the prevalence of heterosexually acquired HIV infections in the UK, including those among pregnant women, and the numbers of new HIV diagnoses reflect the focus of the pandemic in sub-Saharan African countries with close links to the UK. In England, Wales and Northern Ireland, of the HIV-infected heterosexual patients receiving care in 2003 (and for whom ethnicity was reported), 70 per cent were black-African. Over two-fifths of the HIV-infected heterosexuals receiving care reside and are treated outside London; most of these are black-African. Among women who were born in sub-Saharan Africa and who subsequently gave birth in the UK, an estimated one in 42 were HIV-infected in 2003. However, the transmission of HIV from mother to child in the UK has been reduced greatly since the universal offer and recommendation of HIV testing in pregnancy was introduced. Despite this, undiagnosed HIV infection and late diagnosis of longstanding HIV infection continue to be a feature of the treatment histories of black-African men and women, particularly among those attending GUM clinics outside London. Of women born in sub-Saharan Africa attending eight GUM clinics outside London in England, Wales and Northern Ireland, one in 10 had a previously undiagnosed HIV infection.

INJECTING DRUG USERS (IDU)

In addition to laboratory and clinicians' reports there are also data on the prevalence of hepatitis C, hepatitis B, and HIV from the Unlinked Anonymous Prevalence Monitoring Programme Survey of HIV and Hepatitis in Injecting Drug Users. Overall HIV infection remains relatively rare among IDUs in the UK although there is evidence of ongoing and possibly increased transmission. The prevalence of HIV among IDUs has remained substantially higher in London than the rest of the country. Needle- and syringe-sharing increased in the late 1990s, and since then has been stable, with around one in three IDUs reporting this activity in the last month. The sharing of other injecting equipment is more common, whilst few IDUs wash their hands or swab injecting sites prior to injecting. Over 4,000 reported cases of HIV occur in the population of intravenous drug users and this accounts for 6.5 per cent of HIV diagnosis up to 2003.

SEX WITH A KNOWN HIV-POSITIVE PARTNER

The risks associated with individual unprotected sexual exposure with an HIVpositive partner are shown below: these are the estimated risk per incident with someone who is HIV-positive, and may help the clinician in discussing the risk to the index patient. In addition to the factors discussed below (Table 4) the risk of transmission may also be affected by the integrity of the anogenital epithelium and the presence of sexually transmissible infections.The risk per act is probably higher for an individual with multiple HIV-positive partners than it is for those in monogamous relationships.

It is not necessary always to discuss these figures with a patient, although if patients do ask questions about transmission risk, they may be used at your discretion. It is important that if you are using these figures in the pre-test discussion they are put into an appropriate context, and it is emphasised that these are only theoretical risks. They are of more use for the clinician, as they can act as a guide to the likelihood of infection.

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