主动发现病例(ACF)在结核病(TB)控制中可能很有价值,但是在不同的环境中,它的最佳实施仍然存在问题。例如,涂片显微镜检查遗漏了多达一半的结核病例,然而是便宜的,检测到最具传染性的结核病例。什么,然后,是使用更敏感和更具体的增量价值,更昂贵,在高负载环境下,ACF中的XpertMTB/RIF等测试?
我们构建了TB的动态传输模型,校准为与印度的城市贫民窟人口一致。我们应用此模型来比较初始症状筛查后2种假设方法的潜在成本和影响:(i)采用类似显微镜的测试的“中等准确性”测试(即,更低的成本,但也更低的准确性)用于细菌学确认和(ii)采用类似Xpert测试的“高精度”测试(更高的成本,但也更高的准确性,同时还检测到利福平抗性)。结果表明,使用中等精度测试的ACF实际上比使用高精度测试的成本更高。在200万贫民窟人口中,根据2000万美元的说明性预算,相对于通过中等准确度测试避免的每例病例,高准确度测试将避免1.14例(95%可信区间0.75-1.99,p=0.28)病例.测试特异性是关键驱动因素:在5%的显著性水平下,高精度测试将更具影响力。只要高准确度测试的特异性比中等准确度测试高至少3个百分点。促进高精度测试影响的其他因素是:(i)其检测利福平耐药性的能力可导致二线治疗的长期成本节省;(ii)其更高的灵敏度有助于ACF避免的总体病例。在这项研究的局限性中,我们的成本模型只关注测试和治疗的商品成本;我们的估计不应被视为ACF总成本的指标。ACF中的涂片和Xpert样测试等测试的真正特异性仍然存在不确定性,关于在这种条件下参考标准的准确性。
我们的结果表明,更便宜的诊断不一定转化为成本更低的ACF,因为从测试成本中节省的任何费用都可能被包括假阳性结核病治疗在内的因素所抵消,灵敏度降低,并放弃二线治疗的节省。在资源有限的设置中,因此,在为ACF设计具有成本效益的策略时,必须考虑所有这些因素。
Active
case finding (ACF) may be valuable in tuberculosis (TB) control, but questions remain about its optimum implementation in different settings. For example, smear microscopy misses up to half of TB cases, yet is cheap and detects the most infectious TB cases. What, then, is the incremental value of using more sensitive and specific, yet more costly, tests such as Xpert MTB/RIF in ACF in a high-burden setting?
We constructed a dynamic transmission model of TB, calibrated to be consistent with an urban slum population in India. We applied this model to compare the potential cost and impact of 2 hypothetical approaches following initial symptom screening: (i) \'moderate accuracy\' testing employing a microscopy-like test (i.e., lower cost but also lower accuracy) for bacteriological confirmation and (ii) \'high accuracy\' testing employing an Xpert-like test (higher cost but also higher accuracy, while also detecting rifampicin resistance). Results suggest that ACF using a moderate-accuracy test could in fact cost more overall than using a high-accuracy test. Under an illustrative budget of US$20 million in a slum population of 2 million, high-accuracy testing would avert 1.14 (95% credible interval 0.75-1.99, with p = 0.28) cases relative to each
case averted by moderate-accuracy testing. Test specificity is a key driver: High-accuracy testing would be significantly more impactful at the 5% significance level, as long as the high-accuracy test has specificity at least 3 percentage points greater than the moderate-accuracy test. Additional factors promoting the impact of high-accuracy testing are that (i) its ability to detect rifampicin resistance can lead to long-term cost savings in second-line treatment and (ii) its higher sensitivity contributes to the overall cases averted by ACF. Amongst the limitations of this study, our cost model has a narrow focus on the commodity costs of testing and treatment; our estimates should not be taken as indicative of the overall cost of ACF. There remains uncertainty about the true specificity of tests such as smear and Xpert-like tests in ACF, relating to the accuracy of the reference standard under such conditions.
Our results suggest that cheaper diagnostics do not necessarily translate to less costly ACF, as any savings from the test cost can be strongly outweighed by factors including false-positive TB treatment, reduced sensitivity, and foregone savings in second-line treatment. In resource-limited settings, it is therefore important to take all of these factors into account when designing cost-effective strategies for ACF.