The effect of changing the definition of AIDS on the modeling of AIDS

Costs of HIV+/AIDS at CD4+ counts disease stages based on treatment protocols

We report treatment protocols for HIV+/AIDS patients by CD4+ counts (T-lymphocyte cells/mm3: > or = 500, 499-200, 199-50, and < 50) as a tool to provide better definition and to project annual costs (total charges for services) and lifetimes costs for HIV+/AIDS. The treatment protocols, derived from the literature and an HIV+/AIDS Physician Panel, defined the resource use associated with antiretroviral therapy and opportunistic disease prophylaxis and treatment. Resource use costs were derived from the published literature, insurance database, Medicare fee schedules, surveys, and the Physician Panel. At CD4+ counts, the rates of opportunistic diseases were derived from the Physician Panel experience; the mean occupancy times were derived from the literature. The sensitivity analysis indicated stability of the lifetime costs to variation in mean occupancy times, rates of opportunistic diseases, rates of adverse events (AE), and costs. The total annual costs (1995 dollars) of HIV+/AIDS patients ranged from $1,934 (> or = 500), $6,015 (200-499), and $9,031 (50-199), to $25,239 ( < 50). The annual costs of opportunistic diseases are esophageal candidiasis (EC) ($2,194), tuberculosis (TB) ($2,924), cryptococcal meningitis (CM) ($17,264), toxoplasmosis ($17,631), Mycobacterium avium complex (MAC) (+20,153), Non-Hodgkin's lymphoma (NHL) ($22,329), wasting syndrome ($26,676), central nervous system (CNS) lymphoma ($27,333), Pneumocystis carinii pneumonia (PCP) [mild ($3,545), moderate ($4,889), and severe ($32,609)], Kaposi' sarcoma (KS) [mild/moderate ($5,902), and severe ($10,744)], and cytomegalovirus (CMV) retinitis ($100,337). The projected lifetime costs of HIV+/AIDS are $94,726 (annual costs $7,645). Our lower lifetime costs as compared with recent estimates may be due to including resources only for HIV+/AIDS-related treatment and not for non-HIV+/AIDS conditions, as well as reduced resource use resulting from more efficient diagnostic and therapeutic techniques and earlier prophylaxis provided by experienced HIV+/AIDS physicians. Nonetheless, our estimates are consistent with decreasing costs of HIV+/AIDS due to a reduction in the average length of stay and frequency of hospitalizations as well as to replacement of inpatient care by outpatient services.

A meta-analysis of estimates of the AIDS incubation distribution

Information from 12 studies is combined to estimate the AIDS incubation distribution with greater precision than is possible from a single study. The analysis uses a hierarchy of parametric models based on a four-parameter generalized F distribution. This general model contains four standard two-parameter distributions as special cases. The cases are the Weibull, gamma, log-logistic, lognormal distributions. These four special cases subsume three distinct asymptotic hazard behaviors. As time increases beyond the median of approximately 10 years, the hazard can increase to infinity (Weibull), can plateau at some constant level (gamma), or can decrease to zero (log-logistic and lognormal). The Weibull, gamma and 'log-logistic distributions' which represent the three distinct asymptotic hazard behaviors, all fit the data as well as the generalized F distribution at the 25 percent significance level. Hence, we conclude that incubation data is still too limited to ascertain the specific hazard assumption that should be utilized in studies of the AIDS epidemic. Accordingly, efforts to model the AIDS epidemic (e.g., back-calculation approaches) should allow the incubation distribution to take several forms to adequately represent HIV estimation uncertainty. It is recommended that, at a minimum, the specific Weibull, gamma and log-logistic distributions estimated in this meta-analysis should all be used in modeling the AIDS epidemic, to reflect this uncertainty.