The drug warfare being waged on the HIV virus could end up making the epidemic worse, scientists have warned.

Aids patients typically take a cocktail of powerful drugs to keep on top of the infection. However, it is feared that some patients will become sloppy about taking these pills, allowing resistance to build up.

This situation has already arisen with common antibiotics. Years of inappropriate prescription by doctors and failure of patients to take their drugs properly has led to the emergence of so-called "superbugs" that resist virtually everything modern medicine has in its armoury.

There is now a possibility that HIV could develop the same way, according to Sally Blower of the University of California San Francisco.

She presented the findings of her research to the annual meeting of the American Association for the Advancement of Science (AAAS) in Anaheim.

She said that poor discipline was a problem even in carefully controlled clinical trials. Some people were observed not to take their medication in the way instructed and this gave the virus a chance to mutate into drug-resistant forms.

Mathematical models

Blower and her colleagues used advanced mathematical models and data from clinical drug trials, to show the course of the Aids epidemic.

When mathematicians take this rate and apply it to what is known about how people take drugs in day-to-day life, Blower said the picture is a grim one.

"It could have beneficial effects, but it is also likely that if treatment increases, the likelihood of drug resistance increases," Blower said.

"If we increase treatment rates considerably and keep a tight, tight rein on how (the drugs) are handed out, you would have a beneficial effect on 15% of new infections." In other words, 15% of new HIV infections, on average over 10 years, would be prevented.

But if someone does not monitor patients very closely, Blower's model predicts a 20% increase in new infections over 10 years.

"There is going to be drug resistance and we've got to expect that," Blower added, pointing out that antibiotic-resistant forms of tuberculosis have existed since the 1950s.