Health officials yesterday called for a safe sex campaign aimed at the middle-aged after a sharp rise in sexually transmitted infections in the over-45s.

Cases more than doubled among the age group between 1996 and 2003, according to figures compiled from 19 sexual health clinics by the Health Protection Agency.

Doctors said the rise could be a result of more older people being single or beginning new relationships and being less likely to use condoms because there was a much lower risk of pregnancy. Internet dating and drugs for impotence were also likely to play a role, they added.

Researchers examined records at clinics in the West Midlands and identified 4,445 cases among people aged 45 and over, most of them straight men and women. Cases of chlamydia, herpes, warts, gonorrhoea and syphilis all rose sharply, with overall infection rates per 100,000 of population rising from 16.7 to 36.3.

The most common infection - 45% of all cases - was genital warts, with herpes next at 19%. Among men, those aged 55 and older were most likely to have an infection, while rates among women were highest in the 45 to 54 age group, according to the study, which appears in the journal Sexually Transmitted Infections.

"Sexual health strategies have rightly focused on the under-25s but our results indicate that sexual risk-taking behaviour is ... also an increasing trend in the over-45s," said Babatunde Olowokure, a consultant epidemiologist who led the study at the HPA's regional surveillance unit in Birmingham.

In 1996, the over-45s accounted for only 3.9% of all visits to sexual health clinics, but by 2003 this had risen to 4.5%.