From the Mycobacteriology Research Centre (Drs Velayati and Farnia), National Research Institute of Tuberculosis and Lung Disease (NRITLD), Shahid Beheshti University of Medical Sciences; and the Division of Pulmonary and Critical Care (Dr Mirsaeidi), University of Illinois at Chicago.
CORRESPONDENCE TO: Mehdi Mirsaeidi, MD, MPH, Division of Pulmonary, Critical Care, Sleep, and Allergy, Department of Medicine M/C 719, University of Illinois at Chicago, 840 S Wood St, Chicago, IL 60612-7323; e-mail: email@example.com
FUNDING/SUPPORT: This study was supported by National Research Institute of Tuberculosis and Lung Disease of Iran. Dr Mirsaeidi was supported by the National Institutes of Health [Grant 5 T32 HL 82547-7].
FINANCIAL/NONFINANCIAL DISCLOSURES: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.
We appreciate Dr Click for providing a critique on our publication in CHEST.1 We agree that our article introduces a new potential route of TB transmission that needs urgent consideration.
We performed all possible procedures to avoid laboratory cross-contamination in our study. We confirmed our findings by resampling from locations with positive mycobacterial results. In addition, finding no evidence of matching genotype between human and environmental isolates from the study locations makes the risk of contamination negligible. Consequently, we would confidently confirm our findings in this study.
Regarding the role of animals in this epidemiologic cycle, we addressed the potential role of animals in transmitting Mycobacterium tuberculosis, particularly multidrug-resistant TB, to humans elsewhere.2 Given that Tehran is a rat-infested city, the role of the rats in contaminating the environment with M tuberculosis should be investigated. To our knowledge, the prevalence of M tuberculosis in animals has not been studied in Iran.
The contamination of water samples with sewage is very unlikely in Tehran for a couple of reasons. The water samples were mainly collected from channels that are designed to collect superficial water from streets after rains and have no connection to sewage. Besides, voiding in water channels is not culturally accepted in Iran, so the risk of direct contamination also is very unlikely. We still think that water source contamination could occur through expectoration.
Regarding TB lymphadenitis, we did not match environmental isolates with all isolates from TB lymphadenitis from Tehran. Considering we could not isolate any M tuberculosis from drinking water samples, and no one drinks channel water, at least in the study locations, the role of drinking M tuberculosis was not questioned for us. We agree this possible association should be investigated in other locations where the risk of drinking contaminated water is valid.
Finally, we agree with Dr Click that our understanding about TB transmission is evolving. In our previous studies,3,4 we showed M tuberculosis has a high biologic adaptation in response to difficult environmental conditions, including exposure to antibiotics. This ability allows M tuberculosis to stay alive and infectious in soil and water for a significant duration of time; as we showed, it remains alive in wet soil for > 9 months.
Role of sponsors: The sponsors had no role in the design of the study, the collection and analysis of the data, or the preparation of the manuscript.
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