The cost-effectiveness of routine tuberculosis screening with Xpert MTB/RIF prior to initiation of antiretroviral therapy: a model-based analysis

Abstract

Background: In settings with high tuberculosis (TB) prevalence, 15-30% of HIV-infected individuals initiating antiretroviral therapy (ART) have undiagnosed TB. 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 TB/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 cell count = 171 cells/μl; TB prevalence 22%). We simulated no active screening and four diagnostic strategies, smear microscopy (sensitivity 23%); smear and culture (sensitivity, 100%); one Xpert sample (sensitivity in smear-negative TB: 43%); two Xpert samples (sensitivity in smear-negative TB: 62%). Outcomes included projected life expectancy, lifetime costs (2010 US$), and incremental cost-effectiveness ratios (ICERs). Strategies with ICERs less than $7100 (South African gross domestic product per capita) were considered very cost-effective.

Results: Compared with no screening, life expectancy in TB-infected patients increased by 1.6 months using smear in symptomatic patients and by 6.6 months with two Xpert samples in all patients. At 22% TB prevalence, the ICER of smear for all patients was $2800 per year of life saved (YLS), and of Xpert (two samples) for all patients was $5100/YLS. Strategies involving one Xpert sample or symptom screening were less efficient.

Conclusion: Model-based analysis suggests that screening all individuals initiating ART in South Africa with two Xpert samples is very cost-effective.

Figure 1. Component costs of care for the first year after screening

Breakdown of the first year of health care costs for an individual initiating ART in South Africa in the Xpert-2-All strategy, a time frame which total costs may be compared for some budgetary purposes. Total per person costs were $3,990. TB: tuberculosis. ARV: antiretroviral.

Figure 2. One-way sensitivity analysis of model parameters

One-way sensitivity analysis comparing the impact of key model parameters on the incremental cost-effectiveness ratio (ICER) of the Xpert-2-all strategies, compared to the next best, non-dominated strategy. The x-axis is the ICER. Each horizontal bar represents a parameter varied over the range indicated; wider bars indicate larger differences in the ICER seen by varying the parameter. ‘x’ following a number denotes a multiplicative effect on the baseline value of parameter. MDR: Multidrug-resistant; DS: Drug-susceptible; FLD: First-line drugs; SLD: Second-line drugs; YLS: year of life saved.

Figure 3. Two-way sensitivity analysis of TB prevalence and mortality of untreated TB on the incremental cost-effectiveness ratio (ICER) for Xpert

The lower horizontal line indicates the 2010 per capita GDP of South Africa ($7,100), which the WHO defines as ‘very cost-effective’ (see Methods). The upper horizontal line indicates three times the per capita GDP of South Africa ($21,300), which is considered a ‘cost-effective’ intervention.