By Liz Highleyman

Some individuals who are newly infected with HIV and have never received treatment are already resistant to some antiretroviral drugs, due to the transmission of resistant virus (known as primary resistance). Two recently published studies looked at the prevalence of primary resistance in highly disparate settings.

In the first study, published in the October 2007 issue of AIDS, researchers performed systematic resistance testing of individuals in Switzerland with documented HIV seroconversion between 1996 and 2005 who had available samples with a viral load above 1000 copies/mL obtained within 1 year of estimated seroconversion.

Viral sequences from 822 individuals were available. HIV risk groups were men who have sex with men (42%), heterosexual contact (32%), and injection drug users (20%).

Resistance interpretation used the Stanford list of mutations for surveillance of transmitted drug resistance and the French National Agency for AIDS Research algorithm.

Results

·         The overall prevalence of transmitted resistance was:

o        7.7% for any drug;

o        5.5% for nucleoside reverse transcriptase inhibitors (NRTIs);

o        1.9% for non-nucleoside reverse transcriptase inhibitors (NNRTIs);

o        2.7% for protease inhibitors.

·         2% of patients had transmitted resistance to 2 or 3 antiretroviral drug classes.

·         No significant trend in prevalence of transmitted resistance was observed over the study period.

·         There were no differences in prevalence of primary resistance according to race/ethnicity, risk group, or sex, but prevalence was highest among individuals with HIV subtype B.

“The transmission rate of drug-resistant HIV-1 has been stable since 1996, with very rare transmission of dual- or triple-class resistance,” the authors wrote. “These data suggest that transmission of drug resistance in the setting of easy access to antiretroviral treatment can remain stable and be kept at a low level.”

In the second study, researchers performed genotypic resistance testing on viral isolates from 100 recently infected (between 2002 and 2006) antiretroviral-naive individuals in Abidjan, Côte d'Ivoire.

Here, the overall prevalence of HIV-1 variants with resistance mutations to NRTIs, NNRTIs, PIs, or fusion inhibitors was 6%.

Together, these studies indicate that the prevalence of primary resistance is low (6-8%), but occurs often enough to warrant concern. Some experts in Europe and the U.S. recommend resistance testing before a patient starts treatment, but this may not be feasible in resource-limited settings.

References