The annual conference of the Public Health Laboratory Service heard that the growing problem of resistance made measures to prevent initial HIV infection ever more important.

This does not meant that they cannot be treated, but it does mean that the range of drugs available to treat them is reduced

Dr Deenan Pillay

Dr Deenan Pillay, of the PHLS Antiviral Susceptibility Reference Unit in Birmingham, told the conference that experts had long suspected HIV patients might begin to develop resistance to drugs after they had been receiving treatment for some time.

"However we now know that resistant strains can be transmitted from one person to another, meaning that patients can be carrying drug-resistant strains from the moment they are infected," he said.

"This does not meant that they cannot be treated, but it does mean that the range of drugs available to treat them is reduced."

On-going problem

Dr Pillay said that resistance, once established, appeared, in most cases, to remain.

Among five patients who had been infected with resistant HIV, in four of them the resistant element persisted for up to three years.

He said: "Although this is a small study, it further highlights the potentially serious impact of HIV resistance."

Dr Pillay said the development of new drugs was vital as nobody knew how long existing therapies would be able to keep HIV in check.

But he added: "HIV is an entirely preventable disease and now more than ever we need to ensure that the prevention message are heeded.

"Safer sex is the key to preventing HIV."

Herpes

Another study presented at the conference has found that among HIV patients in south London there were high levels of Herpes simplex virus 2, which puts them at increased risk of transmitting HIV.

The study found that among 800 HIV patients in south London, 71% were infected with HSV-2.

Dr Anna Maria Geretti, of the PHLS in south London said: "We already know that if a patient with HIV is also infected with HSV-2, the virus which causes genital herpes, they are at increased risk of transmitting HIV to a sexual partner even if they have no herpes symptoms.

"Doctors may wish to consider offering HIV patients the opportunity to be tested for HSV-2 so that those who are infected can be made aware of the increased risk of transmission."