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Cause of Sputum Acid-Fast Smear-Positive: Mycobacterium tuberculosis or nontuberculous mycobacterium
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Li-Na Lee, Doctor Laboratory Medicine, National Taiwan University Hospital, Jann-Yuan Wang, Po-Ren Hsueh, Chong-Jen Yu, I-Shiow Jan, Li-Na Lee, Pan-Chyr Yang
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linalee{at}ntu.edu.tw Li-Na Lee, et al.
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To the Editor: We read with great interest the study of Field et al (June 2006)1 on lung disease due to nontuberculous mycobacteria (NTM). They review the common manifestations of and conditions associated with NTM lung disease in area with low incidence of tuberculosis (TB). This issue is even more complicated in endemic area of TB. NTM are causing increasing numbers of infections in Taiwan.2,3 The proportion of patients with NTM in all with smear-positive sputum in our hospital increased dramatically in recent years (9.3% in 2001, 21.1% in 2002, 20.7% in 2003, 20.9% in 2004, 23.3% in 2005, and 34.7% in 2006). From September 2005 to June 2006, a total of 100 new patients with smear- positive sputum (fluorochrome methods) were identified. Sixty-five were culture-positive for Mycobacterium tuberculosis (MTB group). Of the other 35 patients (NTM group), 30 (85.7%) were culture-positive for NTM, including M. avium intracellulare complex in 11, M. abscessus in 5, M. fortuitum in 4, mixed M. abscessus and M. chelonae in 4, M. chelonae in 2, M. kansasii in 1, mixed M. avium intracellulare complex and M. kansasii in 1, and unidentified mycobacterial species in 2. Of the remaining 5 patients, multiple samples (at least six) of sputum were all culture- negative for mycobacteria. Based on the disease criteria established recently,4 16 patients had NTM infection, including M. avium intracellulare complex infection in 8, M. abscessus infection in 3, M. abscessus and M. chelonae infection in 3, and one each for M. fortuitum and M. kansasii infection. Smear positivity was more likely due to NTM in patients with underlying bronchiectasis (100%) or old pulmonary TB (58.3%). Dyspnea was significantly associated to TB (85%), whereas weight loss was more likely to occur in NTM group (54.5%). The radiographic findings were significant different between the two groups. Smear-positivity was more likely due to M. tuberculosis in patients with fibroexudative (80.6%) or consolidative (76.2%) pattern, or predominantly upper-lung-field involvement, and more likely due to NTM in patients with normal findings (90.9%). Pulmonary cavitation was significantly associated with TB (91.3%). Consistent with previous reports5 and the study of Field et al,1 smear- positivity was more likely due to NTM in patients with underlying lung disease such as bronchiectasis, old pulmonary TB, and pulmonary fibrotic change. Although the two groups have some differences, none of them is diagnostic. The increasing proportion of NTM patients in all with smear- positive sputum points out the necessity of applying a rapid and specific test (such as direct amplification assay) for identification of M. tuberculosis in smear-positive sputum. References 1. Field SK, Cowie RL. Lung disease due to the more common nontuberculous mycobacteria. Chest 2006; 129:1653-1672 2. Lai CC, Lee LN, Ding LW, et al. Emergence of disseminated infections due to nontuberculous mycobacteria in non-HIV-infected patients, including immunocompetent and immunocompromised patients in a university hospital in Taiwan. J Infect 2006; 53:77-84 3. Ding LW, Lai CC, Lee LN, et al. Disease caused by non-tuberculous mycobacteria in a university hospital in Taiwan, 1997-2003. Epidemiol Infect 2006:1-8 4. Griffith DE, Aksamit T, Brown-Elliott BA, et al. An official ATS/IDSA statement: diagnosis, treatment, and prevention of nontuberculous mycobacterial diseases. Am J Respir Crit Care Med 2007; 175:367-416 5. Wickremasinghe M, Ozerovitch LJ, Davies G, et al. Non-tuberculous mycobacteria in patients with bronchiectasis. Thorax 2005; 60:1045-1051 |
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