An official American Thoracic Society and Infectious Disease Society of America statement has shown that patients with pulmonary complex (MAC) disease who complete 10–12 months of negative cultures on therapy but then have either single or multiple positive MAC cultures are more likely to have reinfection with a new MAC strain.

Case presentation:

A 63‐year‐old woman was diagnosed with pulmonary disease caused by clarithromycin (CAM)‐susceptible MAC. Before initiating chemotherapy using a four‐drug regimen containing CAM, an investigation of the patient’s residential bathroom was conducted and one of the isolates recovered from the bathtub inlet was found to be genetically identical to sputum‐derived isolates by variable number tandem repeats analysis using tandem repeat loci (MATR‐VNTR). A second investigation of the bathroom during chemotherapy showed no isolates, and five consecutive sputum cultures were negative for 12 months until chemotherapy was discontinued. A recurrence occurred 3 months after the end of chemotherapy (at age 65 years). A third investigation of the bathroom was performed and MATR‐VNTR analysis revealed that the VNTR profile of the isolates recovered from the sputum at recurrence was identical to that of the isolates recovered from the sputum at initial diagnosis and the bathroom at the first investigation.


The recurrence occurred due to endogenous reactivation of the initial isolate despite drug treatment for 12 months after sputum culture conversion. Further genetic analyses of MAC isolates recovered from patients and environments should be encouraged.

  • This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/).

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