Rationale: Serial smear analysis to guide respiratory isolation (RI) of patients with suspected tuberculosis (TB), the majority of whom will be found not to have TB, leads to expensive and unnecessary isolation, and may potentially result in decreased vigilance of subjects with respiratory compromise.
Objectives: To compare the performance of a single first-sputum, Mycobacterium tuberculosis-specific nucleic acid amplification (NAA) test with three sputum smears for assessing the need for RI.
Methods: Prospective evaluation of 493 patients with suspected TB (74% HIV positive) admitted to RI in a major county hospital in the United States, who had at least three sputum smears and material available from the first sample for additional NAA testing.
Measurements and main results: Accuracy of the first sputum NAA result and serial smears for identifying patients with potentially infectious TB who truly require RI was determined. Forty-six patients (9.3%) had TB confirmed by culture. First-sputum NAA test detected all patients with TB who had a positive smear (n = 35), even when the first of the three specimens was smear negative. In addition, when compared with serial smears, the first-sputum NAA had a higher sensitivity (0.87; 95% confidence interval [CI], 0.74-0.95) and specificity (1.0) in the detection of subjects with positive M. tuberculosis cultures (smear sensitivity, 0.76; 95% CI, 0.61-0.87; and specificity, 0.96; 95% CI, 0.94-0.98).
Conclusions: A single first-sputum NAA testing can rapidly and accurately identify the subset of patients with suspected TB who require RI according to serial sputum smears. Its potential use to shorten RI time does not preclude the need to obtain subsequent specimens for culture.