Using Markov processes to describe the prognosis of HIV-1 infection

In 1989, Turner and colleagues proposed a new method for automated classification and prediction of outcomes for hospitalized patients with AIDS, based on severity of illness. The authors have confirmed this system, which includes three main stages and 20 substages, in a cohort of HIV-1-infected symptomatic patients admitted to the Miami Veteran's Affairs Medical Center (VAMC) since 1988. They propose a new model of Markov illness-and-death processes and use it to describe the disease progression of the patient cohort. The new Markov model also measures transitions between stages, including risk factors associated with the speed of transitions. Significant differences in survival experiences were found from the different disease stages. The estimated mean (median) survival times were: from stage 1, 21.0 (17.8) months; from stage 2, 10.5 (8.4) months; and from stage 3, 6.7 (4.7) months. In addition, age at HIV-1 diagnosis and homosexual behavior were significant prognostic factors for disease progression and survival. The results indicate that the combination of a severity-of-illness clinical staging system with Markov illness-and-death process modeling is particularly useful for the evaluation of prognostic factors influencing the course of HIV-1 disease progression.