HIV infection among over-50s has more than doubled in seven years.
The number of new cases recorded in England, Wales and Northern Ireland rose from 299 in 2000 to 710 in 2007, research has shown. Half were diagnosed late, increasing the risk of an early death from Aids.
Compared with younger adults carrying the virus, older people were significantly more likely to have been infected through sex with men. Older "straight" adults were more likely to acquire the virus in the UK, but there was evidence of white heterosexual men picking up the infection abroad.
The findings were published online in the journal AIDS.
Health Protection Agency data shows there are more than 83,000 people in the UK who have HIV. Study co-author Valerie Delpech, the HPA's head of HIV surveillance, said cases in over-50s accounted for only 8 per cent of new diagnoses. But she said "anybody is at risk of HIV infection if they do not use protection and practise safe sex".