Background:  How best to determine trends in transmitted HIV drug resistance is an important public health question—whether clinical genotype reporting, analysis of research cohort studies, or sentinel-site prevalence monitoring is most representative is unknown. The San Francisco Department of Public Health has been conducting site and population prevalence monitoring for transmitted drug resistance since 2004.

Methods:  We compared the prevalence of drug resistance in 3 sentinel populations:  those with newly identified infection of unknown duration identified at an anonymous HIV testing center; those with acute HIV infection (HIV antibody^–/RNA⁺), and those with non-acute newly identified infection at the city municipal sexually transmitted diseases (STD) clinic. Antiretroviral drug-resistance was measured by sequence analysis (Trugene HIV-1 Genotyping Kit) and categorized according to International AIDS Society (IAS) Guidelines 2006.

Results:  Of 225 new HIV cases, 70 were from the anonymous HIV testing center; 15 were acute, and 140 were non-acute from the STD clinic. The table shows the frequency of resistance by class, period, and population. Resistance to 2 classes was identified in 5 cases; no cases had ≥3 class resistance. While the number of resistant cases was low, there were no differences in the distribution of resistance between populations or by time.

Conclusions:  Transmitted drug resistance was modest in frequency and not increasing in newly identified HIV cases in San Francisco. Given that anonymous testers and those with acute or long-standing HIV infection had similar rates of drug resistance, sentinel-site surveillance appears to be a robust and potentially generalizable means of drug-resistance monitoring.