NEW DELHI, 27 February 2008 (PlusNews) - The silence and taboo surrounding anal sex is putting millions of men and women at risk of HIV, delegates attending the fourth international microbicides conference in New Delhi, India, heard this week.

Often thought of as strictly a "gay thing", studies are showing that anal intercourse is also part of heterosexual coupling, and is largely unprotected, said Jim Pickett, chair of International Rectal Microbicide Advocates (IRMA), which released a report on the subject at the conference.

The report, Less Silence, More Science warned that researchers could no longer afford to ignore anal sex - one of the biggest drivers of the epidemic - and called for more research into the development of a rectal microbicide.

"We must consider the possibility that unprotected anal intercourse, even when practiced rarely, may in fact be a significant source of HIV transmission in many contexts," the report said. Women were also likely to engage in anal sex in cultures and regions where virginity was especially prized and contraception was not easily available.