Article Type : Research Article
Volume : 5
Issue : 2
Online ISSN : 2581-4761
Print ISSN : 2581-4753
Article First Page : 116
Article End Page : 122
Introduction: Tuberculosis continues to be the leading cause of morbidity and mortality in developing nations. Off late infections due to mycobacterial species other than tubercle bacilli are being reported frequently. Nontuberculous mycobacteria are being increasingly recognized and isolated as pathogens from immunocompetent host too. They are found in both pulmonary and extrapulmonary form of disease. The prevalence of infections due to NTM is known to vary with place, host and climatic factors.
Aim: the present study is a retrospective cross-sectional observational study for a period of two years from Jan.2013- Dec.2014, at Princess Era Hospital,a teaching hospital of Deccan college of medical sciences at Hyderabad. Data from microbiology lab records was retrieved and analysed.
Materials and Methods: about 232 specimens from 229 patients with clinical symptoms of tuberculosis were analysed for laboratory diagnosis of nontuberculosis mycobacterial infection in mycobacteriology section of microbiology laboratory. Seventy nine samples were obtained from 78 patients with pulmonary form of disease and 153 samples were from 151 patients with extrapulmonary form of disease. Study was approved by ethical committee of the college and patient consent was obtained prior to sample collection. All the specimens received in the laboratory were processed by direct microscopy for acid fast bacilli using Ziehl Neelsen stain. Culture was performed on conventional LJ media and Middle Brook 7H12 media in MGIT 320 automated system. Identification of culture positive isolates was achieved by standard biochemical test and rapid immunochromatography test for detection of mycobacterial tuberculosis protein 64 antigen [MPT64].
Results: Direct microscopy was positive in 20.52%. and 4.25% of which were later identified as NTM. Culture yielded positive result in 22.27% of the subjects. NTM were isolated in 3.49% of the total subjects studied. Mycobacterium tuberculosis was the most common isolate as 84.31%, both in pulmonary and extrapulmonary form of disease as 76.92% and 92%. NTM were isolated in 15.68% of culture positive samples. Majority of the NTM’s were from pulmonary specimens as 75% and rest from extrapulmonary specimens as 25%. In subjects above 50 years of age, NTM was more prevalent in men. The most common predisposing risk factor was chronic obstructive lung disease with bronchiectasis in majority and cavitary lesion in one. And pleural effusion in rest as 25%. In the present study only rapid growers were isolated and M. chelonae was the predominant species 87.5% followed by M.fortuitum in 12.5%. Sputum yielded maximum NTM’s as 50%, BAL as 25% followed by pleural fluid and pleural biopsy as 12.5% each. MPT64 antigen test and Para Nitro Benzoic acid resistance at 500ug/ml concentration were found to be very useful presumptive test for identification of NTM. Samples in duplicate where ever feasible were obtained and processed for NTM; and all yielded the same microbe confirming the etiological role.
Conclusion: NTM infection in symptomatic subjects was seen in significant proportion of the culture positives. Therefore, laboratories performing mycobacterial culture should be equipped with facilities for identification and drug susceptibility test for NTM in order to provide proper diagnosis and targeted therapy. Failure to do so may increase the chances of them being misinterpreted and reported as MDR-TB.
Keywords: Mycobacteria tuberculosis, Nontuberculosis mycobacteria, MPT64 antigen, Para nitrobenzoic acid, Pulmonary form of disease, Extra pulmonary form of disease.