Important note: Information in this article was accurate in September 2001. The state of the art may have changed since the publication date.AIDSWEEKLY Plus; Monday, September 17 & 24, 2001
Staff Medical Writers
NewsRx - The number of drug-resistant HIV cases has already reached epidemic proportions in San Francisco, but transmission of drug-resistant strains is not to blame, reports a new UCLA/UCSF study in the September 2001 issue of Nature Medicine.
"The good news is that transmission of drug-resistant HIV will not become a major public health problem," said Dr. Sally Blower, lead author and UCLA professor of biomathematics and AIDS Institute member. "The bad news is that the prevalence of drug-resistant HIV is already high and will continue to substantially increase."
Antiretroviral drugs currently offer the best means for controlling the progression and symptoms of HIV disease. But combination drug therapy, or the triple-drug "cocktail," demands a complicated dosage regimen that is difficult to maintain and often provokes severe side effects.
According to the authors, physicians treating people with HIV may unwittingly contribute to the drug-resistant epidemic if they don't recognize the risks associated with incorrect use of the antiretroviral medications.
"These drugs are as dangerous as chemotherapy," warned Dr. James Kahn, UCSF associate professor of medicine and last author of the study. "General practitioners should not be using them. You really need a skilled HIV specialist to prescribe the medications and closely monitor the patient's adherence and response to treatment."
Blower's team used a mathematical model to understand the evolution of drug-resistant HIV strains in the San Francisco gay community from 1996 to 2001, and to predict the epidemic's growth from 2001 to 2005.
Their theoretical model included such variables as the number of infected drug-sensitive cases, the treatment rate, increases in risky sexual behavior, and the rate at which drug-resistant strains of HIV emerge during treatment. Blower's team modeled the evolution of 1,000 different strains of drug-resistant HIV.
Blower's team estimated that only 3% of cases in San Francisco were drug resistant in1997. However, by 2005, they predict that 42% of all HIV cases will be drug resistant.
Using their mathematical model, the research team determined that the rise in the number of drug-resistant cases was mainly due to the conversion of drug-sensitive cases to drug-resistant cases during antiretroviral therapy. Sexual transmission of drug-resistant virus did not - and will not - play a major role in fueling the epidemic of drug resistance. Blower's team estimated that in 2000, only 8% of the new HIV drug-resistant infections were due to transmission of resistant strains.
"In the future, the vast majority of new HIV infections will still be drug-sensitive," said Blower, "We predict that even in 2005, only 16% of new infections will be drug resistant." The team also determined that the transmission of drug-resistant strains has not increased, and will not increase, the overall number of new HIV infections.
Blower and her coauthors point out that physicians and policy makers can take steps to minimize the prevalence and the transmission of drug-resistant HIV. Based upon their findings, they recommend four epidemic-control strategies:
Despite the predicted high prevalence of drug resistance, the authors emphasize that people shouldn't consider their findings an argument against antiretroviral drug treatment in San Francisco or in developing countries.
"We have shown that the surging number of drug-sensitive HIV cases - which are due to increases in high-risk sex - pose a substantially greater public health problem than the transmission of drug-resistant virus," Blower noted.
Based on the their findings in San Francisco, the researchers' strongly advocate the expanded use of antiretroviral drugs in developing countries. However, they caution that these therapies must be administered carefully and coupled with effective efforts to reduce the risk of infection.
"Antiretroviral treatment will do the most good when the patient is ready to follow it. But the optimal timing is a real unknown," explained Kahn. "We need scientifically proven guidelines to help HIV specialists work with their patients in making this complicated decision."
The National Institute of Allergy and Infectious Diseases, a branch of the National Institutes of Health, and the University of California AIDS Research Program funded the study. Nick Aschenbach and Hayley Gershengorn, research assistants in Blower's lab, are coauthors on the study.
This article was prepared by AIDS Weekly editors from staff and other reports.
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