Abstract
IntroductionThe Centers for Disease Control and Prevention has recommended using a nucleic acid amplification test (NAAT) for diagnosing pulmonary tuberculosis (TB) but there is a lack of data on NAAT cost-effectiveness.MethodsWe conducted a prospective cohort study that included all patients with an AFB smear-positive respiratory specimen at Grady Memorial Hospital in Atlanta, GA, USA between January 2002 and June 2008. We determined the sensitivity, specificity, and positive and negative predictive value of a commercially available and FDA-approved NAAT (amplified MTD, Gen-Probe) compared to the gold standard of culture. A cost analysis was performed and included costs related to laboratory tests, hospital charges, anti-TB medications, and contact investigations. Average cost per patient was calculated under two conditions: (1) using a NAAT on all AFB smear-postive respiratory specimens and (2) not using a NAAT. One-way sensitivity analyses were conducted to determine sensitivity of cost difference to reasonable ranges of model inputs.ResultsDuring a 6 1/2 year study period, there were 1,009 patients with an AFB smear-positive respiratory specimen at our public urban hospital. We found the NAAT to be highly sensitive (99.6%) and specific (99.1%) on AFB smear-positive specimens compared to culture. Overall, the positive predictive value (PPV) of an AFB smear-positive respiratory specimen for culture-confirmed TB was 27%. The PPV of an AFB smear-positive respiratory specimen for culture-confirmed TB was significantly higher for HIV-uninfected persons compared to those who were HIV-seropositive (152/271 [56%] vs. 85/445 [19%]; RR = 2.94, 95% CI 2.36–3.65, p<0.001). The cost savings of using the NAAT was $2,003 per AFB smear-positive case.ConclusionsRoutine use of the NAAT on AFB smear-positive respiratory specimens was highly cost-saving in our setting at a U.S. urban public hospital with a high prevalence of TB and HIV because of the low PPV of an AFB smear for culture-confirmed TB.
Highlights
The Centers for Disease Control and Prevention has recommended using a nucleic acid amplification test (NAAT) for diagnosing pulmonary tuberculosis (TB) but there is a lack of data on NAAT cost-effectiveness
There is a large burden of disease due to non-tuberculous mycobacteria (NTM) at Grady Memorial Hospital (GMH) given the high prevalence of HIV infection among patients who receive care at the hospital
Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the NAAT performed on acid-fast bacilli (AFB) smearpositive respiratory specimens were calculated using an AFB culture positive for Mycobacterium tuberculosis (MTB) as the reference standard for diagnosis of TB disease
Summary
The Centers for Disease Control and Prevention has recommended using a nucleic acid amplification test (NAAT) for diagnosing pulmonary tuberculosis (TB) but there is a lack of data on NAAT cost-effectiveness. The U.S Centers for Disease Control and Prevention (CDC) has recommended that a nucleic acid amplification test (NAAT) be used routinely for the diagnosis of pulmonary tuberculosis (TB) [1]. GMH provides care to a large number of persons living with HIV. The annual number of TB cases at GMH gradually decreased from .150 in the late 1990s [5] to 40–80 in the last 5 years. Up to 40% of patients with TB at GMH are HIV co-infected. There is a large burden of disease due to non-tuberculous mycobacteria (NTM) at GMH given the high prevalence of HIV infection among patients who receive care at the hospital. Epidemiology of NTM is difficult to define because it is not a reportable disease, the prevalence of NTM has been increasing over the past 30 years [6,7,8]; a high NTM prevalence hampers TB diagnosis by confounding acid-fast bacilli (AFB) smear results
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