Estimating the incubation period of paediatric AIDS in Rwanda

Objective: To estimate the distribution of the incubation period of paediatric AIDS in Rwanda. Design: Data were collected between February 1984 and December 1990 at the Centre Hospitaller de Kigali (CHK), the capital city of Rwanda, Central Africa. Patients: We used a sample of 685 AIDS cases registered consecutively in the Department of Paediatrics of the CHK, in which the proportion of perinatally acquired HIV-1 infection was estimated to be 98.6%. Methods: We performed both non-parametric and parametric analyses. The methods of estimation were adapted to truncated data, using essentially the same methods as Auger ef al. in their analysis of data from the New York City and the New York State AIDS case registries in 1988. Results: We found that a double Weibull model fitted the data very well and that the risk of developing AIDS was high for subjects under 18 months of age, but lower for older subjects. Conclusions: Our results were qualitatively similar to those of Auger et al., There were quantitative differences between the two studies, but it was not possible to compare median survival periods. Parameters such as median or mean survival times cannot be validly estimated using only data from registers because these data exclude infected subjects who have not yet developed AIDS.