EDITORIAL
INT J TUBERC LUNG DIS 18(5):508–508 Q 2014 The Union http://dx.doi.org/10.5588/ijtld.14.0211
Understanding the costs of better tuberculosis diagnostics ADVANCING tuberculosis control will require improved access to modern diagnostic testing in high-prevalence areas. Unfortunately, implementing such testing in lower income countries has been a challenge for a number of reasons. Cost is a key impediment to implementing better diagnostics, as the countries most afflicted by tuberculosis often have the least resources to spend on health care. Understanding the costs associated with specific testing strategies is therefore vital to making good decisions on which tests to implement and how they should be implemented. The article by Yakhelef and colleagues in this issue of the Journal provides important new insights into the costs associated with a potential new diagnostic test, thin-layer agar, in Homa Bay District, Kenya.1 Thin-layer agar is a culture-based test in which Mycobacterium tuberculosis colonies are observed on an agar-based medium. The test is significantly more sensitive than acid-fast smear or culture on Lowenstein-Jensen medium for the detection of tuberculosis,12 but is less expensive than culture in liquid medium (the current quasi-gold standard). A recent meta-analysis demonstrated that thin-layer agar was 87% sensitive in detecting M. tuberculosis and provided a positive result a mean of 11.5 days after the specimen was received (an average of 11.8 days sooner than standard solid medium cultures).3 The meta-analysis specifically highlighted the gaps in knowledge about the costs and feasibility of the thinlayer agar method. The manuscript by Yakhelef et al. fills some of those gaps. The authors prospectively compared two algorithms for the evaluation of acid-fast smearnegative tuberculosis suspects: the standard algorithm at the site, which incorporated chest radiography, clinical examination and empiric antibiotic treatment, and an algorithm using culture on thin-layer agar. The thin-layer agar algorithm detected additional tuberculosis cases compared with the standard algorithm, at an estimated cost of E1477.40 per additional case detected and treated. These costs were particularly sensitive to the proportion of the additional cases who were tracked and started on treatment; if additional cases are found but not treated, the cost per treated
case rises significantly. The authors found, furthermore, that because of local practices, thin-layer agar did not result in any cost savings from stopping treatment among patients with negative cultures. These two findings highlight the importance of considering the costs of diagnostic tests in the setting of programs, rather than in isolation, to better understand the true cost of implementing a test. How does this compare to other diagnostic options? Both solid and liquid medium culture systems were cost-effective compared with acid-fast smears alone in a Brazilian clinic setting, with liquid medium proving more expensive but also more effective.4 In a high-incidence South African setting, liquid culture cost $243.92 (approximately E176) per additional smear-negative tuberculosis case detected; the proportion of patients started on treatment was not specified.5 While the costs from different settings are not entirely comparable, when combined with local data they permit programs to make the best choices with available resources. Additional studies that evaluate diagnostic costs in low-income settings would be welcomed to inform these choices. JASON E. STOUT, MD, MHS Duke University Medical Center Durham, North Carolina USA e-mail: [email protected] References 1 Yakhelef N, Audibert M, Varaine F, et al. Is introducing rapid culture into the diagnostic algorithm of smear-negative tuberculosis cost-effective? Int J Tuberc Lung Dis 2014; 18: 541-546. 2 Battaglioli T, Rintiswati N, Martin A, et al. Comparative performance of Thin Layer Agar and Lowenstein-Jensen culture for diagnosis of tuberculosis. Clin Microbiol Infect 2013; 19: E502-E508. 3 Leung E, Minion J, Benedetti A, Pai M, Menzies D. Microcolony culture techniques for tuberculosis diagnosis: a systematic review. Int J Tuberc Lung Dis 2012; 16: 16–23, i-iii. 4 Dowdy D W, Lourenco M C, Cavalcante S C, et al. Impact and cost-effectiveness of culture for diagnosis of tuberculosis in HIVinfected Brazilian adults. PLOS ONE 2008; 3: e4057. 5 Chihota V N, Grant A D, Fielding K, et al. Liquid vs. solid culture for tuberculosis: performance and cost in a resource-constrained setting. Int J Tuberc Lung Dis 2010; 14: 1024–1031.
INT J TUBERC LUNG DIS 18(5):508–508 Q 2014 The Union http://dx.doi.org/10.5588/ijtld.14.0211
Understanding the costs of better tuberculosis diagnostics ADVANCING tuberculosis control will require improved access to modern diagnostic testing in high-prevalence areas. Unfortunately, implementing such testing in lower income countries has been a challenge for a number of reasons. Cost is a key impediment to implementing better diagnostics, as the countries most afflicted by tuberculosis often have the least resources to spend on health care. Understanding the costs associated with specific testing strategies is therefore vital to making good decisions on which tests to implement and how they should be implemented. The article by Yakhelef and colleagues in this issue of the Journal provides important new insights into the costs associated with a potential new diagnostic test, thin-layer agar, in Homa Bay District, Kenya.1 Thin-layer agar is a culture-based test in which Mycobacterium tuberculosis colonies are observed on an agar-based medium. The test is significantly more sensitive than acid-fast smear or culture on Lowenstein-Jensen medium for the detection of tuberculosis,12 but is less expensive than culture in liquid medium (the current quasi-gold standard). A recent meta-analysis demonstrated that thin-layer agar was 87% sensitive in detecting M. tuberculosis and provided a positive result a mean of 11.5 days after the specimen was received (an average of 11.8 days sooner than standard solid medium cultures).3 The meta-analysis specifically highlighted the gaps in knowledge about the costs and feasibility of the thinlayer agar method. The manuscript by Yakhelef et al. fills some of those gaps. The authors prospectively compared two algorithms for the evaluation of acid-fast smearnegative tuberculosis suspects: the standard algorithm at the site, which incorporated chest radiography, clinical examination and empiric antibiotic treatment, and an algorithm using culture on thin-layer agar. The thin-layer agar algorithm detected additional tuberculosis cases compared with the standard algorithm, at an estimated cost of E1477.40 per additional case detected and treated. These costs were particularly sensitive to the proportion of the additional cases who were tracked and started on treatment; if additional cases are found but not treated, the cost per treated
case rises significantly. The authors found, furthermore, that because of local practices, thin-layer agar did not result in any cost savings from stopping treatment among patients with negative cultures. These two findings highlight the importance of considering the costs of diagnostic tests in the setting of programs, rather than in isolation, to better understand the true cost of implementing a test. How does this compare to other diagnostic options? Both solid and liquid medium culture systems were cost-effective compared with acid-fast smears alone in a Brazilian clinic setting, with liquid medium proving more expensive but also more effective.4 In a high-incidence South African setting, liquid culture cost $243.92 (approximately E176) per additional smear-negative tuberculosis case detected; the proportion of patients started on treatment was not specified.5 While the costs from different settings are not entirely comparable, when combined with local data they permit programs to make the best choices with available resources. Additional studies that evaluate diagnostic costs in low-income settings would be welcomed to inform these choices. JASON E. STOUT, MD, MHS Duke University Medical Center Durham, North Carolina USA e-mail: [email protected] References 1 Yakhelef N, Audibert M, Varaine F, et al. Is introducing rapid culture into the diagnostic algorithm of smear-negative tuberculosis cost-effective? Int J Tuberc Lung Dis 2014; 18: 541-546. 2 Battaglioli T, Rintiswati N, Martin A, et al. Comparative performance of Thin Layer Agar and Lowenstein-Jensen culture for diagnosis of tuberculosis. Clin Microbiol Infect 2013; 19: E502-E508. 3 Leung E, Minion J, Benedetti A, Pai M, Menzies D. Microcolony culture techniques for tuberculosis diagnosis: a systematic review. Int J Tuberc Lung Dis 2012; 16: 16–23, i-iii. 4 Dowdy D W, Lourenco M C, Cavalcante S C, et al. Impact and cost-effectiveness of culture for diagnosis of tuberculosis in HIVinfected Brazilian adults. PLOS ONE 2008; 3: e4057. 5 Chihota V N, Grant A D, Fielding K, et al. Liquid vs. solid culture for tuberculosis: performance and cost in a resource-constrained setting. Int J Tuberc Lung Dis 2010; 14: 1024–1031.
