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To provide information on responses to combination antiretroviral therapy in children, adolescents and older HIV-infected persons.Multicohort collaboration of 33 European cohorts.Forty-nine thousand nine hundred and twenty-one antiretroviral-naive individuals starting combination antiretroviral therapy from 1998 to 2006.Time from combination antiretroviral therapy initiation to HIV RNA less than 50 copies/ml (virological response), CD4 increase of more than 100 cells/μl (immunological response) and new AIDS/death were analysed using survival methods. Ten age strata were chosen: less than 2, 2–5, 6–12, 13–17, 18–29, 30–39 (reference group), 40–49, 50–54, 55–59 and 60 years or older; those aged 6 years or more were included in multivariable analyses.The four youngest age groups had 223, 184, 219 and 201 individuals and the three oldest age groups had 2693, 1656 and 1613 individuals. Precombination antiretroviral therapy CD4 cell counts were highest in young children and declined with age. By 12 months, 53.7% (95% confidence interval: 53.2–54.1%) and 59.2% (58.7–59.6%) had experienced a virological and immunological response. The probability of virological response was lower in those aged 6–12 (adjusted hazard ratio: 0.87) and 13–17 (0.78) years, but was higher in those aged 50–54 (1.24), 55–59 (1.24) and at least 60 (1.18) years. The probability of immunological response was higher in children and younger adults and reduced in those 60 years or older. Those aged 55–59 and 60 years or older had poorer clinical outcomes after adjusting for the latest CD4 cell count.Better virological responses but poorer immunological responses in older individuals, together with low precombination antiretroviral therapy CD4 cell counts, may place this group at increased clinical risk. The poorer virological responses in children may increase the likelihood of emergence of resistance.