Cost-Effectiveness Analysis of the Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test as Used Routinely on Smear-Positive Respiratory Specimens

Abstract

A decision analysis was conducted to evaluate the cost-effectiveness of programs in which the Amplified Mycobacterium Tuberculosis Direct test (MTD) (Gen-Probe) is used to rapidly exclude Mycobacterium tuberculosis complex as a cause of disease in smear-positive respiratory specimens. MTD sensitivity, specificity, and probability of inhibition for smear-positive specimens were estimated from literature reports. Costs and laboratory performance characteristics were determined from review of records and practices at an urban hospital in the mid-Atlantic United States. In the base case, 31.4% of smear-positive specimens were assumed to be culture positive for M. tuberculosis. Under these conditions, the marginal cost of the MTD testing program was estimated as $338 per smear-positive patient, or $494 per early exclusion of tuberculosis based on negative MTD results. By comparison, the cost of respiratory isolation ($27.77/day) and drugs ($5.66/day) averted by MTD testing was estimated at $201 per early tuberculosis exclusion. MTD testing was therefore not costeffective in this scenario. Sensitivity analysis revealed that cost-effectiveness estimates are sensitive to the number of smear-positive specimens processed annually, the relative prevalence of M. tuberculosis in smearpositive specimens, and the marginal daily cost of respiratory isolation. A decision tool is therefore presented for assessing the cost-effectiveness of MTD under various combinations of those three variables. While routine MTD testing of smear-positive specimens is not expected to be cost-saving for most individual hospitals, centralized reference laboratories may be able to implement MTD in a cost-effective manner across a wide range of situations.Tuberculosis (TB) is a leading infectious killer worldwide and is far from elimination as a public health threat in the United States and other developed countries (14,22). Nevertheless, in countries such as France (23), the United Kingdom (12), and the United States (9), incidence rates of TB (caused by Mycobacterium tuberculosis) are beginning to fall relative to rates of disease from mycobacteria other than TB (MOTT), particularly M. avium complex. Rapid diagnosis of TB currently relies on the examination of smears stained for acid-fast bacilli (AFB). However, AFB smears cannot distinguish TB from MOTT. Mycobacterial culture readily differentiates between TB and MOTT, but culture results are often not available for 2 to 3 weeks after specimen collection. Since the sputum AFB smear identifies the individuals who are potentially most infectious, current clinical guidelines are to isolate patients who are suspected to have TB on the basis of sputum smear-positive results in negative-pressure rooms (4) and to place such individuals on presumptive therapy for TB, pending either results from culture or response to therapy. However, MOTT are not typically transmitted from person to person by the respiratory route and do not necessarily respond to antibiotics directed against M. tuberculosis.In recent yea...

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