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Background:  Antiretroviral resistance transmitted to newly infected patients impairs efficacy of HAART. Transmitted resistance implies source patients are receiving incompletely suppressive antiretroviral therapy. Studies in urban populations indicate increasing rates of resistance in patients with primary HIV infection (PHI), suggesting transmission by patients in care but on non-suppressive therapy.

Methods:  The Duke-UNC-Emory PHI Consortium has identified and enrolled patients with acute HIV infection since Jan 1998. PHI is defined by a negative HIV ELISA within 30 days of diagnosis.  Phenotypic (PT) HIV resistance testing was done by Virco Antivirogram. Phenotypic resistance was defined by the following levels of reduced susceptibility: ZDV (4.0); 3TC (4.5); ddI (3.5); ddC (3.5); d4T (3.0); ABC (3.0) NVP (8.0); EFV (6.0); DLV (10.0); RTV (3.5); IDV (3.0); SAQ (2.5); NFV (4.0); APV (2.5). To assess patterns of transmitted resistance from a non-urban setting, we studied patients living in North Carolina identified with PHI between Jan 98 and May 03. Statistical comparisons were by 2-sided Fisher’s Exact Test.

Results:  30 patients with PHI had PT resistance testing during the study. Between January 1998 and June 2000, 4/12 PHI patients (33%) had PT resistance (10 males [6 white, 3 black, 1 Latino], 2 females [2 white]). Since June 2000 there have no cases of PT resistance in 18 PHI patients (13 males [4 white, 8 black, 1 Latino], 5 females [4 black, 1 Latina]), (p = 0.018 for comparison of rates of resistance in the 2 time periods). Transmission risks were, from January 1998 to June 2000:  8 MSM, 4 heterosexuals; June 2000 to May 2003:  8 MSM, 8 heterosexuals, 2 unknown. All 4 samples with resistance were in white MSM. Rates of resistance by transmission risk: MSM 4/16 (25%) vs heterosexuals 0/12 (p = 0.11) and by race: white 4/12 (33%) vs black or Latino 0/18 (p = 0.018).

Conclusions:  Among patients diagnosed with PHI in North Carolina, resistance was significantly more common in whites than in non-whites and occurred significantly more often before Jun 00 than afterwards. No cases of transmitted resistance have been observed over the past 3+ years. These data suggest that new HIV infections are being acquired either from patients without significant antiretroviral resistance (perhaps because fewer patients on therapy have transmissible levels of HIV viremia) or that new infections are transmitted most often by persons not in care or unaware of their HIV status.

Keywords: Acute HIV Infection; Resistance; Transmission