Drug-resistant HIV strains increasing

The rise is thought to be due to patients not being prescribed a high enough dosage of anti-HIV drugs or failing to take their full course.

It may mean that more efforts need to be put into supporting them to follow complicated regimes which can involve taking up to 30 different pills a day.

According to a study of 80 newly-infected people by the Aids Research Center at Rockerfeller University in New York, as many as 16.3% had strains of HIV which were associated with resistance to some treatments.

Some 3.8% appeared to be resistant to several anti-HIV drugs.

Genetic testing

The scientists, led by Dr Daniel Boden, used genetic testing to investigate whether the virus carried by the patients was different to the standard HIV-1 infection prevalent in the US.

They also tested whether the form of the virus carried by 67 of the patients could reproduce in the laboratory when confronted by anti-HIV drugs.

They found that, in 26.8% of cases, the drugs' effectiveness was reduced.

Their study was published in the Journal of the American Medical Association (JAMA).

Cocktails of anti-HIV drugs, known as anti-retroviral agents, have been behind a huge decrease in the death rate from Aids in the West.

But HIV is a highly mutable virus and, unless it is reduced to undetectable levels, it can develop resistance to drug treatments.

Definitions

The scientific world is divided on how to define resistance. The Rockerfeller study took it to be a threefold increase in HIV's ability to withstand a drug.

In another study by the University of California at San Diego, also published in JAMA, it is defined as a 10-fold increase, compared with a laboratory strain of HIV-1.

The California researchers subjected 141 newly-diagnosed patients to genetic testing.

Some 2.1% had strains of HIV which were resistant to one or more anti-retroviral drugs.

More than a quarter of strains studied were between two and a half and 10 times more resistant to one or more drugs.

The researchers call for greater monitoring of the phenomenon.

In an accompanying editorial, Dr Roger Pomerantz of Jefferson Medical College in Philadelphia says the results may warrant genetic testing of anyone found to be resistant to anti-retroviral drugs.

Genetic testing costs thousands of dollars, but he said that, with time, cheaper and simpler tests would be developed.

Doctors believe immediate action is needed to tackle drug-resistant strains to prevent their spread.

Dr Pomerantz added that safer sex messages also needed to be emphasised.

Aids experts say drug resistance has been noted in the UK, but monitoring is not as good as in other Western countries.

They also called for greater efforts to develop new drugs to fight HIV so that the medical world can keep ahead of the virus.