HIV antiretroviral drug resistance surveillance of treatment-naïve, newly diagnosed patients is conducted at two large local laboratories that account for approximately half of all new HIV diagnoses. Primary resistance surveillance allows public health to monitor the prevalence of resistant strains among newly-identified cases without treatment experience, identify drug resistant strains that may have increased fitness, and help inform treatment and prevention recommendations. Multiclass drug resistance (MDR) is defined as high-level drug resistance in more than one antiretroviral drug class. Currently only three of the four classes with licensed antiretrovirals are typically included in resistance testing: protease inhibitors (PI), nucleoside reverse transcriptase inhibitors (NRTI) and non-nucleoside reverse transcriptase inhibitors (NNRTI). MDR may be associated with poorer health outcomes and may reduce treatment options.

Among 459 specimens that have been successfully genotyped to date, approximately 11 percent have any high-level drug resistance. In trend data from VARHS, combined with data from earlier resistance projects, we have found the proportion of treatment-naïve patients with high-level drug resistance to be steady at around 11 percent from 1999 through 2006. NNRTI resistance remains the most common drug class, with resistance detected in 9 percent. This compares to 3 percent for both NRTI resistance and PI resistance. Multiple class drug resistance was detected in 16 (3 percent) patients, and 5 (1 percent) patients had high-level resistance in all three drug classes. Eight people had some resistance in all three classes.

MDR Cluster: As of January 2007, we identified a small cluster of four people infected with highly similar MDR with resistance to all PIs, all NNRTIs and most NRTIs. Three of the four had evidence of recent HIV infection at the time of their diagnosis and all were antiretroviral naïve. All four are men who have sex with men (MSM) with histories of methamphetamine use and sex with multiple, mostly anonymous partners. We are continuing to work with these patients and providers to locate and test sex partners for HIV. To date, all identified partners have been either not infected with HIV or have an HIV infection not related to this MDR cluster. We are now requesting that all local providers inform Public Health – Seattle & King County of all MDR detected in treatment-naïve patients by calling 206-205-1470. We are also working with additional laboratories to expand drug resistance surveillance efforts. Additionally, in response to this cluster and the widespread interest generated from a press release on the cluster February 1st, we are planning a rapid behavioral assessment of MSM in February. This assessment will take place at venues frequented by MSM with HIV or MSM at risk of HIV, including bars, bathhouses, and possibly some medical clinics. Our goal is to find out whether MSM have heard about the cluster, if they think it was important, and if they plan to, or have made any behavior changes as a result of hearing about the cluster.

HIV treatment guidelines from the United States Department of Health and Human Services recommend drug-resistance testing after a positive HIV test. There is an even stronger recommendation that resistance testing be done prior to the initiation of antiretroviral treatment. Guidelines are available at: aidsinfo.nih.gov/contentfiles/adultandadolescentgl.pdf. For HIV-infected individuals, testing for HIV drug resistance allows clinicians to determine a course of treatment to optimize viral response.