HIV infections among the over-50s have more than doubled in seven years, it was revealed today.
The number of new cases per year recorded in England, Wales and Northern Ireland rose from 299 to 710 between 2000 and 2007, research has shown.
Half were diagnosed late, increasing the risk of an early death from Aids.
Among younger age groups, a third have the HIV infection identified at a similar level of progression.
During the study period, three quarters of deaths among HIV-infected people aged 50 and over occurred within a year of diagnosis.
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.
Ruth Smith, a senior HIV scientist at the Health Protection Agency's Centre for Infections, said: "We estimate that nearly half of older adults diagnosed between 2000 and 2007 were infected at age 50 or over and this highlights the importance of HIV testing - whatever your age.
"We must continually reinforce the safe sex message - using a condom with all new or casual partners is the surest way to ensure people do not become infected with a serious sexually transmitted infection such as HIV."
The findings are published online in the journal AIDS and were presented today at the International Aids Conference in Vienna.
HPA data shows there are more than 83,000 people in the UK living with HIV, a quarter of whom do not know they are infected.
In 2008 there were 7,382 new HIV diagnoses in the UK with an estimated 32% over the age of 15 being diagnosed late.
A late diagnosis of HIV infection is defined as having a CD4 white blood cell count of less than 200 cells per cubic millimetre of blood. Healthy individuals have CD4 counts of 500 and above.
CD4 cells are a key part of the immune system. When their numbers fall too low, a person becomes vulnerable to infection.
Study co-author Valerie Delpech, head of HIV surveillance at the HPA, said: "Although adults aged 50 and over account for just 8% of all new HIV diagnoses, the fact that cases have more than doubled in recent years serves as a timely reminder that anybody is at risk of HIV infection if they do not use protection and practise safe sex.
"HIV remains a serious infection particularly when diagnosed late. The fact that we've seen an increase in the number of older adults getting diagnosed, and in particular getting diagnosed late, highlights the need for raised awareness in that age group."
"Medical guidelines issued in 2008 encouraged widespread testing in areas where there is a high prevalence of HIV and the HPA fully supports any NHS or charity organisation initiative which will encourage increased testing and increased offering of testing across the UK."Reuse content