Incubation period of vertically acquired AIDS in Europe before widespread use of prophylactic therapies.

European surveillance data on vertically acquired (VA) AIDS cases were used to investigate the incubation period of AIDS in the absence of widespread prophylactic treatment and to assess the uncertainty associated with parametric estimates based on retrospective data. Nonparametric and parametric analyses, taking into account the effects of data truncation, were based on a total of 792 children diagnosed with AIDS between July, 1982, and June, 1990, inclusive. Among HIV-infected children who develop AIDS within 8 years, the nonparametric estimate of the median age at diagnosis was 34 months. If 20% of children are assumed to develop AIDS by the age of 1 year (a plausible estimate on the basis of published cohort data), the estimated median among all maternally HIV-infected children is 4.4 years, with 26% of children expected to remain AIDS free by 8 years of age. Results from the parametric (double Weibull) model support the hypothesis of a bimodal distribution, with a subgroup of children progressing rapidly to AIDS at a median age of approximately 5 months. However, neither the relative size of this group nor the median age at which AIDS develops in the remaining children can yet be estimated with any reasonable precision.