Epidemiology of AIDS--statistical analyses

Some central questions concerning the epidemiology of AIDS are addressed by statistical analyses. Applying standard maximum likelihood theory to reported cases of transfusion-associated AIDS in the US, the mean and standard deviation of incubation time for AIDS are estimated to be about 60 and 19 months, respectively. If these parameters are applied to the data from the San Francisco CDC cohort study, we find a good correspondence between estimated and reported cases of AIDS when the probability factor p is 0.27-meaning that about 27% of those infected with HIV are expected to develop AIDS during a period of 8-10 years. Application of the incubation time model and the probability factor p to the data on transfusion-associated AIDS makes it possible to estimate the number of transfusion-associated infections with HIV from 1978 to 1984. These estimates give an exponential increase in the number of cases, with a relative increase of 2.74 each year. It seems reasonable to assume that this increase reflects the spread of the virus within this period.