Clinical Relevance of Nontuberculous Mycobacteria, Oman

Little is known about the clinical relevance of nontuberculous mycobacteria (NTM) in the Arabian Peninsula. We assessed the prevalence and studied a random sample of isolates at a reference laboratory in Muscat, Oman. NTM cause disease in this region, and their prevalence has increased.

N ontuberculous mycobacteria (NTM) are common inhabitants of the environment and have been cultured from water, soil, and animal sources worldwide. NTM are opportunistic pathogens, mostly affecting patients with preexisting pulmonary disease such as chronic obstructive pulmonary disease or tuberculosis (TB), or those with systemic impairment of immunity. The latter group includes those with HIV infection, those using immunosuppressive drugs, and those with leukemia (1).
Because NTM are common in the environment and resistant to commonly used disinfectants, they can be present in nonsterile patient material such as sputum and contaminated medical equipment (bronchoscope washers or samples in the laboratory) and consequently cause pseudoinfection (1,2). To distinguish pseudoinfections from NTM disease and establish the clinical relevance of isolated NTM, the American Thoracic Society (ATS) has published diagnostic criteria (1).
Studies on the clinical relevance of NTM have traditionally been restricted to western countries, where the incidence of TB is relatively low. More recently, research has been initiated in African and East Asian countries (1)(2)(3)(4)(5). There have been no recent reports on isolation and clinical relevance of NTM on the Arabian Peninsula. We analyzed a random sample of NTM isolated from clinical samples in Oman by using molecular techniques. Their clinical relevance was retrospectively analyzed by applying the updated ATS diagnostic criteria for NTM disease (1).

The Study
Prevalence of NTM at the Central Public Health Laboratory (CPHL), the national TB reference laboratory of the Ministry of Health in Muscat, Oman, was assessed by using a laboratory database. The CPHL Institutional Review Board reviewed and approved this study. The CPHL Thirteen samples were randomly selected from all NTM isolated at CPHL during January 2006-September 2007. Selected NTM were subjected to molecular identification at the Dutch National Mycobacteria Reference Laboratory (National Institute for Public Health and the Environment, Bilthoven, the Netherlands). To identify NTM, after eliminating isolates of the M. tuberculosis complex by using the GenoType MTBC assay (Hain Lifesciences, Nehren, Germany), we used the Inno-Lipa Mycobacteria version 2 reverse line blot (Innogenetics, Ghent, Belgium). Both assays were used according to the manufacturer's instructions. If no species-specifi c result was obtained, additional sequencing of the hypervariable region A of the 16S rDNA gene was performed (6).  (Table). One sample could not be identifi ed beyond the M. avium-intracellulare-scrofulaceum complex level because insuffi cient DNA was available for further analyses. Because our molecular identifi cation method does not distinguish M. marinum from M. ulcerans, we performed a light exposure test, which identifi ed yellow colony pigmentation typical for M. marinum. One sample yielded M. tuberculosis and M. intracellulare (Table).
We assessed the clinical relevance of isolates from 13 patients in a retrospective study by applying ATS diagnostic criteria and scoring demographic and clinical data. Results are detailed in the  (Table). Information on predisposing conditions was not available for most patients, although a destroyed lung on chest radiographs suggested previous pulmonary disease. One patient was HIV positive, and another patient had a relapse of pulmonary NTM disease.
Eight patients began treatment, mostly with fi rst-line treatment for TB. Three patients with pulmonary MAC disease and 1 with M. marinum skin disease received regimens that included macrolides, fl uoroquinolones, or both. Therapy resulted in clinical improvement in all but 1 patient. Most patients are still receiving treatment.

Conclusions
A total of 9% all Mycobacterium-positive cultures at CPHL in Muscat, Oman, yielded NTM. Although this conclusion is based on limited data, the prevalence of NTM seems to be increasing in Oman. Few studies are available, but this increase may be true for the entire Middle East region.
Eight of 13 patients met the ATS diagnostic criteria; this fi nding probably refl ects a selection bias because CPHL is a reference laboratory. Nevertheless, these fi ndings indicate that NTM in Oman and throughout the Middle East region is a serious issue that requires attention by clinicians and microbiologists.
Most isolates were MAC members (9/13, 69%), a predominance also noted in previous studies in the United States, Europe, and west Asian countries (25%) (1,8), and South Korea (48%) (9)  isolates in the random sample. Previous North American studies have suggested that M. intracellulare is the more common pulmonary pathogen within the MAC (1). We identifi ed 3 pulmonary samples as MAC-A strains, which were recently elevated to species level as M. chimaera (7). Two samples were clinically relevant. Although M. chimaera has been assumed to be highly virulent (7), a recent study in Germany found only 3.3% of 90 M. chimaera isolates to be clinically relevant (10). M. colombiense was fi rst described as a causative agent of mostly disseminated disease in HIV patients from Colombia (11) and was recently isolated from a child with lymphadenopathy in Spain (12). Its isolation in other countries and from respiratory samples in HIV-negative patients has not been reported. Isolation of M. simiae is a serious concern because this species has been reported to be prevalent in the Middle East (1), and HIV-associated disease has been reported in the region (13).
Most patients in our study received standard treatment for TB. Although treatment should be prolonged and pyrazinamide discontinued because of natural resistance to pyrazinamide in NTM, the choice of fi rst-line treatment for TB, without companion drugs such as macrolides or fl uoroquinolones, is supported by a recently published trial of the British Thoracic Society (14).
In summary, NTM are a serious issue in Oman and their prevalence may be increasing. Our random sample demonstrates that MAC isolates are most frequently isolated. True NTM disease, on the basis of ATS diagnostic criteria, was diagnosed in 62% of the patients assessed. Isolation of NTM is clinically relevant on the Arabian Peninsula and warrants further study.