They are also more than twice as likely to die within a year of their HIV test as are younger people, even if they are diagnosed late.

We have a group of people who don't get tested because they don't think they are at risk, said Dr. Valerie Delpech, of the U.K. Health Protection Agency Center for Infections in London, who worked on the study.

She said the number of HIV-infected Britons has tripled over the past decade, reaching more than 55,000 in 2007. While older adults account for only about one in six of these cases, the number of new diagnoses is growing faster among those aged 50 and older.

The numbers are still small, said Delpech, whose findings appear in the journal AIDS; she estimated fewer than one in 1,000 Britons were infected with HIV. But everyone can be at risk, and we need to think about that, Delpech said.

From 2000 to 2007, the number of newly diagnosed people over 50 jumped from 299 to 710. Compared with their younger peers, older people with HIV were more likely to be gay, white men.

It wasn't all gay men, Delpech stressed. In fact, there were a large proportion of heterosexual men and women.

Almost half of them were diagnosed at advanced stages of the disease. Fourteen percent of these people had died a year later, compared to only one percent of those tested promptly.

What this means is that screening is particularly important in people over 50, said Dr. Anupam B. Jena of Massachusetts General Hospital in Boston, who was not involved in the study.

The take home point from this paper is that it always makes sense to be screening younger people for HIV, but that maybe the balance should shift a little bit toward older people, he said.

In an earlier study of sexually transmitted diseases, Jena found that 60-year-old men taking the erectile dysfunction drug Viagra had twice the rate of STDs of their non-medicated peers. (See Reuters Health story of July 6, 2010.)

While the reasons were unclear, he said more divorces and better health might have conspired to boost sexual prowess and activity among graying heads.

He said the new study made it clear for the first time that the growing number of HIV-positive seniors wasn't just due to people living longer with newer, more effective medicines. In fact, the researchers were able to show that about half of those diagnosed after their 50th birthday had also been infected at age 50 or older.

Delpech said everybody should consider getting tested if they are gay, have been abroad and had sex with locals, or have started a new relationship. If diagnosed promptly at age 30, she said people could easily live to 75 at this point.

It's not all bad news, she added. If you are diagnosed early there are highly effective medicines.

India Medicine Aids