Clinical relevance of Mycobacterium chelonae–abscessus group isolation in 95 patients
Introduction
For a long time Mycobacterium chelonae and Mycobacterium abscessus have been thought to represent the subgroups of a single species, due to overlap in biochemical and genetic properties; only in 1992 M. abscessus was granted a separate species status, supported by DNA-DNA hybridization of less than 70%.1 This taxonomical status was recently changed, when subsets of isolates formerly identified as M. abscessus were elevated to separate species status, as Mycobacterium bolletii and Mycobacterium massiliense, based on <97% rpoB gene sequence homology.2 In the Netherlands, the M. chelonae–abscessus group bacteria are the most frequently encountered rapidly growing nontuberculous mycobacteria (NTM), making up 55% of all referred rapid growers. (Source: National Mycobacteria Reference Laboratory).
In general, NTM are opportunistic pathogens and pulmonary infections mostly affect patients with pre-existing pulmonary disease. Extrapulmonary disease generally occurs after trauma or in patients with systemic impaired immunity, i.e., immunosuppressive medication, HIV infection or hematological malignancy.3 Improvements in laboratory facilities for culture and species identification, increasing notification, and growing awareness of their pathogenic potential have led to increased interest in the NTM in general.3M. abscessus infections in cystic fibrosis (CF) patients, and the problematic resistance of these bacteria to antimycobacterial drugs, have received special attention.1, 3, 4, 5, 6
The environment is the suspected source of infections by NTM, as person-to-person transmission has not been proven.3, 4 Bacteria of these species have been recovered from water and soil.1, 3 Their presence in water and resistance to common disinfectants can result in pseudo-outbreaks due to contamination of laboratory materials7 or medical equipment such as bronchoscopes.8 Hence, clinical M. chelonae, M. abscessus, M. massiliense or M. bolletii isolation, especially from the respiratory tract, does not represent disease per se. To aid in the differentiation between NTM disease and pseudo-infection or contamination, the American Thoracic Society (ATS) provides diagnostic criteria, summarized in Box 1, with a specific emphasis on M. abscessus.3
In the current study we establish the clinical relevance of M. chelonae, M. abscessus, M. massiliense and M. bolletii isolation by studying the clinical and demographical data of patients from whom these species were isolated and determining the percentage of patients that meets the ATS criteria.
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Methods
We retrieved the medical records of all patients in the Netherlands from whom M. chelonae or M. abscessus was isolated between January 1999 and January 2005. We recorded demographical, clinical and microbiological data and status according to the diagnostic criteria by the ATS.3
All patient isolates had been subjected to laboratory diagnosis at the National Institute for Public Health and the Environment (RIVM, Bilthoven, the Netherlands), the national reference laboratory. All isolates had been
Results
We found 95 patients, of whom 56 had M. chelonae, 25 had M. abscessus, 8 had M. massiliense and 6 had M. bolletii isolates. The baseline characteristics of all 95 patients are detailed in Table 1. Thirty-five patients (37%) met ATS criteria for NTM disease. Patients with M. abscessus isolates are significantly more likely to meet ATS diagnostic criteria than those with the other three species combined (p = 0.005; OR 3.8; 95%CI 1.4–9.7).
Seventy-four patients (78%) had isolates obtained from
Discussion
Thirty-seven percent of all patients with M. chelonae–abscessus group isolates have NTM disease as defined by the ATS criteria; patients with M. abscessus isolates are significantly more likely to meet the ATS criteria. Among patients with pulmonary isolates, 27% (20/74) meets ATS criteria. This percentage differs by species; M. abscessus is most relevant (50%; 9/18), followed by M. massiliense (29%; 2/7), M. bolletii (20%; 1/5) and M. chelonae (18%; 8/44). CF patients are specifically affected
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