High prevalence of subtype F in newly diagnosed HIV-1 persons in northwest Spain and evidence for impaired treatment response.

HIV-1 non-B subtype variants were found in 37.8% of 296 newly diagnosed persons in northwest Spain over the past 5 years. Subtype F was the most prevalent non-B subtype (29.6%) and displayed preferential transmission among MSM. Virologic response rates to antiretroviral therapy were lower among F subtypes compared to B subtypes at weeks 24 (31% vs. 78.3%), 48 (51.7% vs. 85.2%), and 96 (61.1% vs. 94.3%) of therapy. Subtype F was independently associated with virological response at 24 weeks.