Anna Vassall from the London School of Hygiene and Tropical Medicine discusses a recently published analysis of the potential health and economic consequences of implementing Xpert MTB/RIF in southern Africa.
In this week’s PLoS Medicine, Nick Menzies and colleagues find that, although the use of Xpert MTB/RIF is likely to be cost-effective in Southern Africa, it may have a substantial impact on Anti-retroviral (ARV) and Multi-drug Resistant Tuberculosis (MDR-TB) treatment costs. The inclusion of population health impact and ARV cost increases the cost-effectiveness ratio of Xpert MTB/RIF compared to previous work examining the cost and consequences for a TB suspect cohort only. The question ‘Is Xpert MTB/RIF cost-effective?’ is now answered incorporating the related question of ‘Is the consequential scale-up of treatment of those who are co-infected with TB and HIV, or have MDR-TB cost-effective?’
Nick Menzies and colleagues are correct to address this broader consideration in their analysis of Xpert MTB/RIF. Most economic evaluations for health interventions only partially model costs and consequences; and thus efficiency. However, improving health in one area often creates a ripple effect, impacting health systems, the economy and society more broadly. In practice, the challenge for any cost-effectiveness analysis is where to draw the line? Should economists evaluating TB interventions also consider the impact on costs associated with diabetes for example? What health systems costs and consequences should be taken into account when examining the cost-effectiveness of an intervention that may require substantial investment to scale up? The standard guidance is that all substantial and measureable effects should be included – but this is interpreted in different ways. In practice, the boundaries are often set by the decision to be made. If ARV or MDR-TB treatment were already fully scaled up in the countries modelled, then their inclusion would be less relevant, but unfortunately they are not.
However, the expansion of the analytical framework for Xpert MTB/RIF to include ARV costs raises an important equity issue. In terms of comparing interventions, each life year or DALY averted remain equal to one another, however each life does not. As those with HIV either cost more, or have shorter lives, treating TB in those with HIV has a higher cost-effectiveness ratio than treating those without HIV. Many TB interventions – that are amongst the most cost-effective public health interventions available – become less so in populations with a prevalence of HIV and MDR-TB. In an environment where many cost-effective interventions are not fully funded, this may have little consequence for resource allocation within those populations, but may matter when allocating resources across the wider population – and challenges many people’s definition of fairness. Therefore the results of analyses of non-HIV interventions that include ARV costs need to be carefully balanced with equity considerations.
The job of a good economic evaluation is not to dictate decisions, but to inform them. Nick Menzies and colleagues have done an excellent job in terms in highlighting the key economic trade-offs for those deciding to employ Xpert MTB/RIF. The inclusion of broader costs in their model implicitly raises important questions about how to design, present and interpret economic evaluations of TB interventions in populations with a high prevalence of HIV in the future.
Anna Vassall is a health economist working with the Social and Mathematical Epidemiology (SAME) group, with the department for Global Health and Development at the London School of Hygiene and Tropical Medicine; researching the economics of HIV, TB and Sexual and Reproductive Health.
The author declares she has no conflict of interest
Xpert MTB/RIF Papers published in PLOS Medicine:
- Population Health Impact and Cost-Effectiveness of Tuberculosis Diagnosis with Xpert MTB/RIF: A Dynamic Simulation and Economic Evaluation. Menzies NA, Cohen T, Lin H-H, Murray M, Salomon JA (2012) PLoS Med 9(11): e1001347.
- Rapid Diagnosis of Tuberculosis with the Xpert MTB/RIF Assay in High Burden Countries: A Cost-Effectiveness Analysis. Vassall A, van Kampen S, Sohn H, Michael JS, John KR, et al. (2011) PLoS Med 8(11): e1001120.
- GeneXpert—A Game-Changer for Tuberculosis Control? Evans CA (2011) PLoS Med 8(7): e1001064.
- Comparison of Xpert MTB/RIF with Other Nucleic Acid Technologies for Diagnosing Pulmonary Tuberculosis in a High HIV Prevalence Setting: A Prospective Study. Scott LE, McCarthy K, Gous N, Nduna M, Van Rie A, et al. (2011) PLoS Med 8(7): e1001061.
- Screening for HIV-Associated Tuberculosis and Rifampicin Resistance before Antiretroviral Therapy Using the Xpert MTB/RIF Assay: A Prospective Study. Lawn SD, Brooks SV, Kranzer K, Nicol M, Whitelaw A, et al. (2011) PLoS Med 8(7): e1001067.
- Is Scale-Up Worth It? Challenges in Economic Analysis of Diagnostic Tests for Tuberculosis. Dowdy DW, Cattamanchi A, Steingart KR, Pai M (2011) PLoS Med 8(7): e1001063.