Background: The BIDUSI study is an ongoing prospective, observational study of the clinical, virologic, and genotypic antiretroviral resistance (GAR) profiles in HIV-positive antiretroviral adherent subjects (SBJs) with detectable plasma viral loads (PVLs) maintained <1,000copies/mL for ³12 consecutive months.

Methods: Antiretroviral adherent SBJ’s were followed from first detectable plasma viral load < 1000 copies/mL. Plasma-derived HIV RNA underwent RTPCR/nested-PCR (35/25-cycles). Standard ddNTP sequencing was employed (ABI Prism 377) reading the protease and first 1Kb of the RT coding regions.

Results: For the 47 SBJs identified the mean duration of low-level viremia  (LLV) was 22 months (12-45) at which time the mean changes in CD4 counts and PVLs were +97 cells/mm³ and +64 copies/mL, respectively. At a mean 16-month follow-up, 7 SBJs had 2 consecutive PVLs >1000 copies/mL (progressors, PGSRs) while 32 SBJs had PVLs which remained <1000 copies/mL (nonPGSRs) up to last F/U (mean 24 months). The differences between these 2 groups at 12 months of LLV are shown in the table. 

		Prior	Prior	Entry	D CD4	Entry	D PVL
		nadir CD4	peak PVL	CD4	at 12months	PVL	at 12months
	n	cells/mm3	copies/mL	cells/mm3	cells/mm3	copies/mL	copies/mL
PGSR	7	104	137,657	395	+114	262	+650
nonPGSR	32	278	50,527	504	+54	393	+22
P value	-	0.01	0.09	0.23	0.5	0.32	0.001

The mean PVL at genotyping was 421 (64-926) copies/mL (n=40) after a mean 14-month LLV. GAR to ³1 on-treatment drugs was observed in 36/40 (90%) SBJs. GAR to all on-treatment drugs was observed in 6/7 (86%) PGSRs and 9/33 (27%) nonPGSRs.

Conclusions: In HIV-infected SBJs antiretroviral therapy may result in a LLV sustained < 1000 copies/mL for prolonged periods and with stable CD4 cell counts. The frequency of GAR in this setting was, however, high (90%). Compared to nonPGSRs, PGSRs were more commonly observed to have ADR to all on-treatment drugs, greater rises in PVLs at 12 months and lower preentry nadir CD4 counts. In SBJs with stable LLV these data highlight the potential utility of GAR testing.