• Ali Akbar Velayati, Parissa Farnia, Mohadese Mozafari, Donya Malekshahian, Amir Masoud Farahbod, Shima Seif, Snaz Rahideh, and Mehdi Mirsaeidi.
• Chest. 2015 Apr 1;147(4):1094-102.

BackgroundThe potential role of environmental Mycobacterium tuberculosis in the epidemiology of TB remains unknown. We investigated the transmission of M tuberculosis from humans to the environment and the possible transmission of M tuberculosis from the environment to humans.MethodsA total of 1,500 samples were collected from three counties of the Tehran, Iran metropolitan area from February 2012 to January 2014. A total of 700 water samples (47%) and 800 soil samples (53%) were collected. Spoligotyping and the mycobacterial interspersed repetitive units-variable number of tandem repeats typing method were performed on DNA extracted from single colonies. Genotypes of M tuberculosis strains isolated from the environment were compared with the genotypes obtained from 55 patients with confirmed pulmonary TB diagnosed during the study period in the same three counties.ResultsM tuberculosis was isolated from 11 of 800 soil samples (1%) and 71 of 700 water samples (10%). T family (56 of 82, 68%) followed by Delhi/CAS (11 of 82, 13.4%) were the most frequent M tuberculosis superfamilies in both water and soil samples. Overall, 27.7% of isolates in clusters were related. No related typing patterns were detected between soil, water, and clinical isolates. The most frequent superfamily of M tuberculosis in clinical isolates was Delhi/CAS (142, 30.3%) followed by NEW-1 (127, 27%). The bacilli in contaminated soil (36%) and damp water (8.4%) remained reculturable in some samples up to 9 months.ConclusionsAlthough the dominant M tuberculosis superfamilies in soil and water did not correspond to the dominant M tuberculosis family in patients, the presence of circulating genotypes of M tuberculosis in soil and water highlight the risk of transmission.

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