Tuberculosis is unique among the major infectious diseases in that it lacks accurate rapid point-of-care diagnostic tests. Failure to control the spread of tuberculosis is largely due to our inability to detect and treat all infectious cases of pulmonary tuberculosis in a timely fashion, allowing continued Mycobacterium tuberculosis transmission within communities. Currently recommended gold-standard diagnostic tests for tuberculosis are laboratory based, and multiple investigations may be necessary over a period of weeks or months before a diagnosis is made. Several new diagnostic tests have recently become available for detecting active tuberculosis disease, screening for latent M. tuberculosis infection, and identifying drug-resistant strains of M. tuberculosis. However, progress toward a robust point-of-care test has been limited, and novel biomarker discovery remains challenging. In the absence of effective prevention strategies, high rates of early case detection and subsequent cure are required for global tuberculosis control. Early case detection is dependent on test accuracy, accessibility, cost, and complexity, but also depends on the political will and funder investment to deliver optimal, sustainable care to those worst affected by the tuberculosis and human immunodeficiency virus epidemics. This review highlights unanswered questions, challenges, recent advances, unresolved operational and technical issues, needs, and opportunities related to tuberculosis diagnostics.
Background In settings with high tuberculosis prevalence, 15–30% of HIV-infected individuals initiating antiretroviral therapy (ART) have undiagnosed tuberculosis. Such patients are usually screened by symptoms and sputum smear, which have poor sensitivity. Objective To project the clinical and economic outcomes of using Xpert MTB/RIF(Xpert), a rapid tuberculosis/rifampicin-resistance diagnostic, to screen individuals initiating ART. Design We used a microsimulation model to evaluate the clinical impact and cost-effectiveness of alternative TB screening modalities -in all patients or only symptomatic patients - for hypothetical cohorts of individuals initiating ART in South Africa (mean CD4 171/μL; tuberculosis prevalence 22%). We simulated no active screening and four diagnostic strategies: 1) smear microscopy (sensitivity 23%); 2) smear and culture (sensitivity, 100%); 3) one Xpert sample (sensitivity in smear-negative tuberculosis: 43%); 4) two Xpert samples (sensitivity in smear-negative tuberculosis: 62%). Outcomes included projected life expectancy, lifetime costs (2010 USD), and incremental cost-effectiveness ratios (ICERs). Strategies with ICERs <$7,100 (South African gross domestic product per capita) were considered very cost-effective. Results Compared with no screening, life expectancy in tuberculosis-infected patients increased by 1.6 months using smear in symptomatic patients and by 6.6 months with 2 Xpert samples in all patients. At 22% tuberculosis prevalence, the ICER of smear for all patients was $2,800/year of life saved (YLS), and of Xpert (2 samples) for all patients was $5,100/YLS. Strategies involving one Xpert sample or symptom screening were less efficient. Conclusions Model-based analysis suggests that screening all individuals initiating ART in South Africa with two Xpert samples is very cost-effective.
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