Rapid TB Test Could Improve Treatment, Reduce Deaths

Troy Brown

November 26, 2012

A rapid tuberculosis (TB) test could significantly improve treatment and reduce the number of deaths in Southern Africa, according to a study published online November 20 in PLOS Medicine.

Nicolas A. Menzies, a PhD candidate in health policy at the Harvard School of Public Health in Boston, Massachusetts, and colleagues developed a calibrated, dynamic mathematical model to study the potential health and economic effect of implementing the Xpert MTB/RIF (Cepheid) test in Botswana, Lesotho, Namibia, South Africa, and Swaziland. They projected results for 10- and 20-year periods beginning in 2012.

Xpert is an automated DNA test that can identify TB and determine whether or not it is resistant to rifampin in just 2 hours. The World Health Organization has recommended it for use in those at high risk for multidrug-resistant TB (MDR-TB) and/or HIV-associated TB.

The current method of TB diagnosis uses sputum smear microscopy, a method that has limited sensitivity, particularly among patients who have HIV. Culture and antibiotic sensitivity testing is slow and relatively expensive and may not be feasible in high-volume settings.

"For individuals with smear-negative TB, the benefits of Xpert implementation would be immediate, leading to the diagnosis and early treatment of many individuals who would be missed by the conventional diagnostic algorithm," the authors write.

The researchers project that within the first 10 years after implementation of the Xpert test, TB prevalence would be reduced by 186 per 100,000 (95% confidence interval [CI], 86 - 350 per 100,000 [28%; 95% CI, 14% - 40%]), incidence would be reduced by 35 per 100,000 (13 - 79 per 100,000 [6%; 95% CI, 2% - 13%]), and annual TB mortality would be reduced by 50 per 100,000 (23 - 89 per 100,000 [21%; 95% CI, 10% - 32%]) compared with status quo estimates.

The authors project that during the first 10 years of use, the Xpert test will prevent 132,000 (95% CI, 55,000 - 284,000) of the estimated 2.6 million (95% CI, 1.7 - 4.3 million) new TB cases and 182,000 (95% CI, 97,000 - 302,000) of the estimated 1.2 million (95% CI, 0.6 - 2.0 million) TB deaths expected in southern Africa under the status quo.

Scale-up Will Increase Health System Costs

Over the course of 10 years, health system costs are projected to increase by $460 million (95% CI, $294 - $699 million) with the use of Xpert; much of this would result from antiretroviral therapy for patients with HIV who would have improved survival with TB treatment. Costs associated with treatment of MDR-TB, which is expensive, will also rise.

The test provides good value, note the authors. Compared with the status quo, Xpert's estimated cost-effectiveness is $959 (95% CI, $633 - $1485) per disability-adjusted life-year averted over the course of 10 years. Across all countries studied, cost-effectiveness ratios ranged from $792 (95% CI, $482 - $1785) in Swaziland to $1257 (95% CI, $767 - $2276) in Botswana.

Despite the cost-effectiveness, health systems may have difficulty absorbing increased costs associated with improved diagnosis and treatment of TB, the authors note.

"If current guidelines are followed, the adoption of Xpert places three key demands on a health system that are additional to the direct costs of diagnosis: providing first-line TB treatment to the large number of additional pan-sensitive TB cases that will be identified, providing additional HIV treatment to coinfected individuals who will live longer as a result of better TB care, and providing second-line TB treatment to the limited number of individuals diagnosed with drug-resistant TB," the authors explain.

They also caution that these results may not be generalizable in populations in which the HIV rates are significantly different from those in Southern Africa.

Two of the authors were supported in part by funding from UNITAID. One author was also supported by a training grant from the Massachusetts General Hospital's Program in Cancer Outcomes and Training. Two of the authors are members of the PLOS Medicine editorial board.

PLoS Med. Published online November 20, 2012. Full text