Korean J Clin Microbiol KJCM Korean Journal of Clinical Microbiology 1229-0025 The Korean Society of Clinical Microbiology 10.5145/KJCM.2012.15.1.9 Original Article Low-Colony Counts of Nontuberculous Mycobacteria: Clinical Significance Analysis Hong Ki Ho 1 Joo Se-Ick 1 Kim Eui-Chong 1 Shin Sue 2 Roh Eun Youn 2 Yoon Jong Hyun 2 Department of Laboratory Medicine, Seoul National University Hospital, Seoul, Korea. Department of Laboratory Medicine, Seoul National University Boramae Hospital, Seoul, Korea. Correspondence: Jong Hyun Yoon, Department of Laboratory Medicine, Seoul National University Boramae Hospital, 41, Boramae-gil, Dongjak-gu, Seoul 156-707, Korea. (Tel) 82-2-870-2601, (Fax) 82-2-870-2620, slice@paran.com 03 2012 20 03 2012 15 1 9 13 15 06 2011 15 09 2011 19 10 2011 Copyright © 2012 The Korean Society of Clinical Microbiology 2012 Background

Diagnosis of nontuberculous mycobacterium (NTM) is challenging, and clinical, radiological and microbiological criteria should be met. Traditionally, culture results on solid media have been reported semi-quantitatively, but no study exists regarding the clinical significance of low-colony count culture reports. The authors of the present study analyzed the clinical significance of low-colony count specimens of NTM with a greater than three-year follow-up period.

 Methods

A total of 341 clinical isolates were evaluated among the isolates at Seoul National University Hospital and Seoul National University Borame Hospital from October 2005 to September 2006. Colony count less than 50 was considered a low-colony count specimen. Identifications of NTM from all the isolates were performed using a DNA chip (PCR reverse hybridization, LG Life Science, Korea). Clinical significance was analyzed by reviewing the medical records of patients with greater than three years of follow-up data after NTM isolation from respiratory samples.

 Results

NTM lung disease was observed in 27.0% of the patients with low-colony count specimens among 167 patients with respiratory samples, and 70.4% of the patients were treated. The low-colony count patients had less NTM lung disease, longer incubation period, and less acid fast bacilli-positivity than patients with a colony count greater than 50.

 Conclusion

The prevalence of NTM lung disease with a low-colony count specimen was greater than 25%. In a clinical setting, NTM lung disease should not be excluded only on the basis of a low-colony count.

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Mycobacteria isolated from October 2005 to September 2006

Abbreviations: TB, Mycobacterium turberculosis; NTM, nontuberculosis mycobacteria.

Distribution of species of nontuberculous mycobacterium

*M. fortuitum, M. senegalense 3; M. avium, M. abscessus 2; M. avium, M. intracellulare 2; M. intracellulare, M. abscessus 2; M. avium, M. terrae complex 1; M. intracellulare, M. fortuitum 1; M. intracellulare, M. gordonae 1; M. intracellulare, M. terrae complex 1; M. gordonae, M. terrae complex 1, †Mycobacterium Genus but cannot identify the species because the lack of specific probe in DNA chip, ‡DNA chip gave the negative results.

Comparison of characteristics of the patients with the <50 and ≥50 colony-counts in respiratory specimens

*They met both clinical and microbiological criteria, †They met microbiological criteria but did not meet clinical criteria, ‡NTM was isolated, but they did not meet microbiological criteria, §NTM infection was suspicious, but follow-up study was insufficient, ∥Median (minimum-maximum).

Abbreviation: AFB, Acid-fast bacilli.