Background: As antiretroviral therapy is increasingly used in settings with limited resources, key questions about the timing of treatment and use of diagnostic tests to guide clinical decisions must be addressed. Methods: We assessed the cost-effectiveness of treatment strategies for a cohort of adults in Côte d'Ivoire who were infected with the human immunodeficiency virus (HIV) (mean age, 33 years; CD4 cell count, 331 per cubic millimeter; HIV RNA level, 5.3 log copies per milliliter). Using a computer-based simulation model that incorporates the CD4 cell count and HIV RNA level as predictors of disease progression, we compared the long-term clinical and economic outcomes associated with no treatment, trimethoprim-sulfamethoxazole prophylaxis alone, antiretroviral therapy alone, and prophylaxis with antiretroviral therapy. Results: Undiscounted gains in life expectancy ranged from 10.7 months with antiretroviral therapy and prophylaxis initiated on the basis of clinical criteria to 45.9 months with antiretroviral therapy and prophylaxis initiated on the basis of CD4 testing and clinical criteria, as compared with trimethoprim-sulfamethoxazole prophylaxis alone. The incremental cost per year of life gained was $240 (in 2002 U.S. dollars) for prophylaxis alone, $620 for antiretroviral therapy and prophylaxis without CD4 testing, and $1,180 for antiretroviral therapy and prophylaxis with CD4 testing, each compared with the next least expensive strategy. None of the strategies that used antiretroviral therapy alone were as cost-effective as those that also used trimethoprim-sulfamethoxazole prophylaxis. Life expectancy was increased by 30% with use of a second line of antiretroviral therapy after failure of the first-line regimen. Conclusions: A strategy of trimethoprim-sulfamethoxazole prophylaxis and antiretroviral therapy, with the use of clinical criteria alone or in combination with CD4 testing to guide the timing of treatment, is an economically attractive health investment in settings with limited resources.
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