LONDON (Reuters Health) - Around 13 percent of people with HIV (news - web sites) in Britain are resistant to all of the three main classes of antiretroviral drugs compared with only 1 percent in 1996, the Health Protection Agency said.

Publishing figures from the National HIV Resistance Database, the agency said tests on a sample of the 19,312 patients known to be receiving HIV therapy showed that 21 percent had no level of resistance, 24 percent were resistant to one drug class, 43 percent to two drug classes and 13 percent to three classes of drugs.

The agency said in a statement that the percentage of people who had not received any prior drug treatment, but who had been infected with a strain of HIV that was already resistant, had increased from 10 percent in 1996 to 14 percent in 2001, with a provisional figure of 21 percent in 2002.

"This shows us that a number of people are contracting their infection from someone who is receiving or has in the past already received drug therapy," according to the agency.

"Of those patients in whom drug therapy is not working, and therefore have a level of virus in the blood sufficient to perform the resistance test, the percentage who have resistance to any one HIV drug and are therefore experiencing 'treatment failure' has remained stable at around 70-80 percent since 1996.

"Of greatest concern, however, are the number who are resistant to all three available classes of drugs. This percentage has increased from 1 percent in 1996 to 14 percent in 2001. The preliminary figure for 2002 is 13 percent and should be interpreted with caution until the data are complete."