The UK Collaborative

HIV Cohort (CHIC) study was initiated in 2001 and collates routine data on HIV-infected individuals attending some of the largest clinical centres in the UK since 1 January 1996. The project was approved by a Multicentre Research Ethics Committee and by local ethics committees. In accordance with data projection policy, data were provided in a pseudo-anonymized format with all names removed and replaced by first-name initial and a Soundex code derived PD 332991 from the patient’s surname. The criteria for inclusion of an individual in the UK CHIC study are that they are HIV-positive, have attended one of the collaborating centres at any time since 1996 and are aged 16 years or over [19]. The analyses are based on data collected up to 31 December 2009. Participants were eligible for analysis if they were antiretroviral-naïve, started cART after 1997, and had at least one CD4 measurement within the baseline period

(90 days before to 6 days after starting cART) and at least one CD4 measurement 6 months after initiation of cART. Participants were further required to have at least one HIV-1 RNA measurement 6 months after initiation of cART and at least one HIV-1 RNA measurement 0–179 days before every CD4 cell count. Virological failure was defined a priori as an HIV-1 RNA measurement exceeding 1000 HIV-1 RNA copies/mL, regardless of whether a participant had interrupted treatment. CD4 cell counts Selleck INCB024360 were natural log-transformed (zero counts set to 1), to meet assumptions about

stability of the variance with increasing CD4 cell count. The relationship between natural log CD4 cell count and time was modelled as a fractional polynomial; fractional polynomials offer a greater range of curve shapes than linear or quadratic polynomials [20]. Fractional Niclosamide polynomials of one and two degrees with powers −2, −1, −0.5, 0, 0.5, 1, 2, 3 were considered (power zero is interpreted as a natural log transformation), including models with repeated powers. We fitted random-effects models with the intercept and fractional polynomial terms random at the individual level, thus allowing CD4 cell count trajectories to vary between individuals. The best-fitting fractional polynomial was selected by comparing the deviance of different models and the percentage of predicted values within 5% of the observed values (see Appendix S1). Participants were classified by their baseline CD4 count (<25, 25–49, 50–99, 100–199, 200–349, 350–499 and ≥500 cells/μL). Participants with more than one CD4 cell count within the baseline period were classified using the measurement closest to the start of cART.