Variable infectiousness in HIV transmission models

Two different approaches to the encapsulation of temporal variation in the infectiousness of HIV-infected persons, and variability in the incubation period of the disease AIDS, in simple homogeneous mixing models of viral transmission in male homosexual communities are described. The first approach is based on the division of the infected population into a series of subclasses with differing levels of infectivity and different durations of occupancy. The second approach is more mechanistic in character and is based on an attempt to relate changes in viral abundance within an infected person to the likelihood that the disease AIDS develops. Variable incubation is induced by variation in the rate of change of viral abundance in the infected population. Numerical projections of changes in the incidence of AIDS through time, generated from both types of model, are compared with projections based on the assumption of constant infectivity throughout the incubation period of AIDS. Model formulation highlights areas in which more detailed quantitative epidemiological studies are required. Methods of parameter estimation and future research needs are discussed.