The Cost-Effectiveness of Preventing AIDS Complications (CEPAC) International model is a state-transition model of HIV disease in resource-limited settings, with data derived for several country-specific analyses, including South Africa (16 (link), 20 (link), 21 (link)). Briefly, a cohort of hypothetical patients pass one at a time through “health states,” in monthly cycles, from entry into HIV care until death. Health states are defined to be both clinically and economically relevant and are stratified by current CD4 count, current HIV RNA level, and history of opportunistic disease. Opportunistic diseases are categorized into the following groups based on etiology, severity, and similarities in prophylaxis and treatment: mild or severe bacterial infections, mild or severe fungal infections, tuberculosis, toxoplasmosis, non-tuberculous mycobacteriosis, Pneumocystis jiroveci pneumonia, and other mild and severe diseases (5 (link)). Deaths in the model occur from acute opportunistic events (within 30 days of the event), chronic AIDS (not within 30 days of an opportunistic disease), or non-HIV-related causes (22 ).
Effective ART in the model functions to suppress HIV RNA and increase CD4 counts (23 (link), 24 (link)). Above and beyond the beneficial effect of increased CD4 count on opportunistic diseases and chronic HIV-related death (5 (link)), antiretroviral therapy per se results in an additional reduction in opportunistic diseases and chronic HIV-related death, as recently reported in Côte d'Ivoire and in the US (25 (link), 26 (link)). Clinical assessments are assumed to occur every 3 months, and CD4 and HIV RNA testing every 6 months while on therapy, consistent with South African recommendations (27 ). According to current standard of care, the model utilizes two sequential lines of antiretroviral therapy; the second-line is initiated when observed CD4 count decreases by 30% from its peak observed on-treatment level, or when a severe opportunistic disease is observed at least 6 months after initiating therapy (27 ). In accordance with current treatment guidelines, the second regimen for each patient is continued until death (7 , 28 (link)).
Effective ART in the model functions to suppress HIV RNA and increase CD4 counts (23 (link), 24 (link)). Above and beyond the beneficial effect of increased CD4 count on opportunistic diseases and chronic HIV-related death (5 (link)), antiretroviral therapy per se results in an additional reduction in opportunistic diseases and chronic HIV-related death, as recently reported in Côte d'Ivoire and in the US (25 (link), 26 (link)). Clinical assessments are assumed to occur every 3 months, and CD4 and HIV RNA testing every 6 months while on therapy, consistent with South African recommendations (27 ). According to current standard of care, the model utilizes two sequential lines of antiretroviral therapy; the second-line is initiated when observed CD4 count decreases by 30% from its peak observed on-treatment level, or when a severe opportunistic disease is observed at least 6 months after initiating therapy (27 ). In accordance with current treatment guidelines, the second regimen for each patient is continued until death (7 , 28 (link)).
