Latest data for the UK suggest 73,000 people are living with HIV, but between 17,000 and 27,800 are unaware of it.
Worryingly, of 7,800 diagnoses of HIV in the UK in 2006, one in three patients were diagnosed late with a CD4 cell count below 200/mm3, the threshold for starting antiretroviral therapy. These patients are less likely to fully benefit from therapy.
Dr Valerie Delpech, head of HIV surveillance at the HPA, said she backed the letter sent in September by CMO for England Sir Liam Donaldson urging GPs to boost early HIV diagnosis.
'We really need to target GPs who are seeing, for example, black African patients,' said Dr Delpech. 'It may be that when new patients attend a practice that is a time to test for HIV.'
However, testing all patients would not be practical or feasible, she said. GPs should concentrate on those at highest risk.
The latest HPA data shows those most at risk are homosexual men. But HIV transmission between heterosexuals in the UK is also increasing, with people from black ethnic minorities most at risk, says the HPA.
Dr Ewen Stewart, chairman of the RCGP Sex, Drugs and HIV Task Group, said: 'GPs have an important role in increasing levels of HIV testing.
'In order to do this we need to be pro-active about raising the issue of HIV testing with people who may have been at risk and then carrying out the HIV testing in general practice settings.
'Many patients with undiagnosed HIV will be seen in general practice, sometimes for conditions that may be related to their HIV, such as shingles, fungal skin infections and chest infections.
'But they may also attend with unrelated conditions.'
The HPA audit also shows sexual health is getting worse in young adults. Rates of herpes and genital warts have increased in those aged 16 to 24. One in 10 screened for chlamydia test positive for the infection.
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