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Background:  Since the introduction of HAART for HIV, changes in drug options and accumulating clinical experience may have influenced considerably the likelihood of initial treatment success. Combining data from 5 observational HIV cohorts in Europe and Canada, we examined the risk of initial virologic failure of first HAART according to calendar year of starting treatment.

Methods:  We included 4143 subjects who:  started HAART (³ 3 drugs including a protease inhibitor [PI], non-nucleoside reverse transcriptase inhibitor [NNRTI], or abacavir [ABC]) naive to ART from 1996 to 2002, had ³ 1 pre-HAART viral load, and had potential for ³ 1-year follow-up. Virologic failure was defined as viral load > 500 copies/mL using the first viral load from 6 to 12 months after HAART initiation, including: (A) all subjects, missing viral load=failure [n=4143]; (B) all subjects with viral load measurement [n = 3360]; (C) all subjects on ART at viral load measurement [n = 3111].

Results:  The table shows risk of virologic failure by year of starting HAART. Failure risk fell substantially from 1996 to 1999, with evidence of a further decline from 1999 to 2002. The trend was apparent for each analysis but relative changes were greatest for analysis C. Median increase in CD4 /mm³ (pre-HAART to 6 months) rose from 97 in 1996 to 150 in 2002.

Year HAART	N	% with Viral Load Failure 6 to 12 Months			Adjusted* Risk Ratio (95% CI) of Viral Load Failure
		A	B	C	A	B	C
1996	162	40	30	25	1.4 (1.1, 1.9)	1.9 (1.3, 2.7)	2.5 (1.6, 3.9)
1997	841	42	28	23	1.2 (1.1, 1.5)	1.5 (1.2, 1.9)	1.9 (1.4, 2.6)
1998	763	39	22	17	1.1 (0.9, 1.3)	1.2 (0.9, 1.5)	1.4 (1.0, 1.9)
1999#	735	34	18	12	1	1	1
2000	575	31	15	10	0.9 (0.8, 1.1)	0.8 (0.6, 1.0)	0.8 (0.5, 1.1)
2001	599	30	15	8	0.9 (0.7, 1.1)	0.8 (0.6, 1.1)	0.7 (0.4, 1.0)
2002	468	25	12	8	0.7 (0.6, 0.9)	0.7 (0.5, 1.0)	0.7 (0.5, 1.1)

Keywords: virological failure; time trends; antiretroviral therapy