Method. The influence of age at infection on progression of human immunodeficiency virus (HIV) disease to different clinical endpoints was studied among 393 HIV-seropositive adults selected from the French SEROCO cohort; follow-up lasted from January 1988 to November 1994. Selected patients had a known date of infection and were enrolled shortly after seroconversion. Age-associated risk ratios (RR) were estimated using the Cox model (age fitted as a continuous variable and RR expressed for each

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... 10-year increment after adjustment for symptomatic primary infection and sexual preference). Results. Age had a weak influence on progression from the date of infection to the first category B event (crude RR = 1.15; adjusted RR = 1.09; 95% confidence interval [CI] : 0.89-1.36) but a marked influence on progression from the first category B to the first category C event (crude RR = 1.95; adjusted RR = 1.97; 95% CI : 1.37-2.79). Similar results were obtained after adjustment for the CD4 + cell count at enrolment. A qualitative CD4 + cell defect could explain the influence of age, but this remains to be confirmed. Conclusion. Age at infection should be included in the definition of CD4 + cell count thresholds for clinical management and treatment initiation. Risk factors for progression should be assessed according to the different clinical endpoints.