Nontuberculous mycobacteria in respiratory specimens: clinical significance at a tertiary care hospital in the north of Portugal.

Abstract

1. Intern in the Department of Pulmonology, Sao Joao Hospital Center, EPE, Porto, Portugal. 2. Attending Physician. Department of Pulmonology, Sao Joao Hospital Center, EPE, Porto, Portugal. 3. Attending Physician. Department of Clinical Pathology, Sao Joao Hospital Center, EPE, Porto, Portugal. Nontuberculous mycobacteria (NTM) are ubiquitous in the human environment, and more than 150 NTM species have been described to date.(1) When inhaled by susceptible individuals, such as those with chronic lung disease, NTM can lead to chronic, progressive, and sometimes fatal respiratory symptoms. Over the last three decades, the incidence of NTM laboratory isolation and related lung disease has been increasing, surpassing that of tuberculosis in some areas.(1,2) However, the isolation of NTM from respiratory specimens might be due to contamination of specimens or colonization of patients that is transient, not necessarily indicating disease.(1) Here, we report the incidence of NTM isolation in the Pulmonology Department of the Sao Joao Hospital Center, a tertiary care university hospital located in Porto, the second most populous city in Portugal. It is the largest hospital in the northern region and one of the three largest in the country. We retrospectively analyzed patients who were seronegative for HIV and for whom NTM had been isolated in at least one respiratory specimen between January of 2008 and December of 2012. The samples were decontaminated with the N-acetyl-L-cysteine-sodium hydroxide method and inoculated into Middlebrook 7H9 broth medium (BBL Mycobacteria Growth Indicator Tube [MGIT]; Becton Dickinson, Franklin Lakes, NJ, USA), in accordance with the manufacturer instructions. Positive cultures, incubated and monitored in an automated culture system (BACTEC MGIT 960; Becton Dickinson), were examined by smear microscopy with Kinyoun staining for AFB. In the presence of AFB, we used a molecular assay for common mycobacteria and additional species (GenoType Mycobacterium CM/ AS; Hain Lifescience GmbH, Nehren, Germany), in accordance with the manufacturer instructions, to determine the species of the isolates. Demographic, clinical, radiological, and microbiological data were collected. The clinical relevance of the isolation in the respiratory sample was defined in accordance with the current American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) criteria.(3) Two hundred and two patients were included in this study. Of those, 118 (58%) were male. The mean age was 64 years (range, 23-89 years). The main risk factors identified were the underlying structural lung disease, such as COPD, in 73 patients (36%), bronchiectasis, in 62 (31%), and tuberculosis sequelae, in 40 (20%); and nonpulmonary conditions, such as diabetes mellitus, in 18 patients (9%), gastroesophageal reflux disease, in 16 (8%), and receiving immunosuppression therapy, in 12 (6%). Data on environmental exposure were not available. A total of 407 isolates were obtained, and the species were identified in 378 (93%). Of the 407 isolates, 237 (58%) were identified as being within the Mycobacterium avium complex (MAC) group and 141 (35%) were identified as belonging to one of 11 other Mycobacterium species, the remaining 29 (7%) being identified as mycobacteria but not down to the species level (Table 1). These isolates were obtained from sputum samples in 192 (95%) of the patients, bronchial lavage fluid samples in 13 (6%), BAL fluid samples in 7 (4%), a lung biopsy sample in 1 (0.5%), and a gastric aspirate sample in 1