Modeling the Progression of HIV-Infected Persons to AIDS

Abstract

Since people who are infected with HIV seem to progress through various stages or phases towards AIDS and death due to AIDS (Redfield et al., 1986; Seligman et al., 1987), a natural model for this progression is through a sequence of five phases (Hethcote, 1987, 1989; Longini et al., 1989, 1990). The first phase is the pre—antibody period, in which a person is infected, but not antibody seropositive. Some people in this first phase have acute illness. The second phase includes persons who are infected and antibody seropositive, but are asymptomatic. The third phase (symptomatic) occurs when the person develops an abnormal hematologic indicator and/or prodromal illnesses such as persistent generalized lymphadenopathy or oral candidiasis. The fourth phase is clinical AIDS, and the fifth phase is death due to AIDS. In Section 2.1 the asymptomatic and symptomatic phases are subdivided into stages in order to provide enough flexibility to match the HIV prevalence and AIDS incidence data in SF. If the number m of infectious stages is even, then the numbers of asymptomatic and symptomatic stages are equal to (m-2)/2; otherwise, they are (m-3)/2 and (m-1)/2, respectively.