By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

SYNOPSIS: Stopping a nosocomial Mycobacterium abscessus outbreak by eschewing tap water.

SOURCE: Baker AW, Stout JE, Anderson DJ, et al. Tap water avoidance decreases rates of hospital-onset pulmonary nontuberculous Mycobacteria. Clin Infect Dis 2020; Aug. 23. doi:10.1093/cid/ciaa1237. [Online ahead of print].

An outbreak of Mycobacterium abscessus colonization and infection occurred in a new addition at Duke University hospital as a result of contamination of the plumbing system, with consequent exposure of patients to infected water.1 The outbreak was “mitigated” by implementing measures designed to avoid exposure of patients to tap water and by implementing intensified disinfection. Now, the same investigators have performed a follow-up study on this outbreak to analyze the incidence of pulmonary nontuberculous mycobacteria (NTM) infections in intermediate-care patients before and after the introduction of sterile water use.

Strict avoidance of tap water was implemented in three intensive care and one intermediate unit to which new lung transplant recipients were transitioned from a cardiothoracic surgery intensive care unit. Sterile water was substituted for tap water for routine care (e.g., oral care, rinsing of suction catheters, and enteral tube irrigation), while showering was restricted and bathing was performed with waterless products or with sterile water. The use of ice was avoided. Eleven months after implementation of these measures, a number of engineering controls also were implemented.

NTM were isolated from 105 patients, with 137 unique episodes over the entire 29 months of the evaluation, but with a significant decrease in association with the interventions. Thus, the incidence rate of NTM isolation, which was 41.0 episodes per 10,000 patient-days in the 10-month outbreak period prior to the intervention, dropped to 9.9 per 10,000 patient-days during the 19 months of the intervention, for an incidence rate ratio (IRR) of 0.24 (95% confidence interval [CI], 0.17-0.34; P < 0.0001).

Lung transplant recipients accounted for 57% of the 137 episodes, and the incidence rate in this group decreased from 28.6 to 3.3 episodes per 10,000 patient days, with an IRR of 0.12 (95% CI, 0.07-0.20; P < 0.0001). Four different NTM species (M. abscessus, M. chelonea-M. immunogenum, MAC, and M. gordonae) accounted for 93% of the episodes, and there was a significant decrease with each, with M. abscessus decreasing from 16.6 to 2.3 episodes per 10,000 patient-days for an IRR of 0.14 (P < 0.0001). Much of the decrease occurred in association with the period when tap water avoidance was initiated and before various engineering controls were added. Cultures of biofilms from water outlets in the affected units recovered the same NTM, and the prevalence of positive cultures did not change significantly through the period of study.


This study once again demonstrates that tap water may be a source of colonization and/or infection of inpatients, including lung transplant recipients, with NTM, including M. abscessus, as it also is with Legionella spp. This results from the ability of these organisms to grow in biofilm on surfaces within the plumbing system where they may persist while being resistant to eradication methods.

The investigators provided strong evidence that tap water was the source of the outbreak and that avoidance of tap water was the primary means of control. The lack of a decrease in recovery of NTM from tap water outlets throughout the period of study suggests that the added engineering controls had little, if any, effect. It also raises the question of whether patients at risk of pulmonary NTM infections, such as lung transplant recipients and those with cystic fibrosis or non-cystic fibrosis bronchiectasis, should avoid tap water in the community. Of note is that this was recommended for AIDS patients, particularly prior to effective antiretroviral therapy, when many suffered from disseminated MAC infection.

The authors point out that complete tap water avoidance, while effective, is resource intensive and expensive, and they raise the possibility that filters and alternative decontamination procedures might also provide benefit. An accompanying commentary calls for the coordinated intervention of government agencies, advocacy organizations, academia, and the healthcare industry, in addition to the currently increasing establishment of water management programs at acute care hospitals.2


  1. Baker AW, Lewis SS, Alexander BD, et al. Two-phase hospital-associated outbreak of Mycobacterium abscessus: Investigation and mitigation. Clin Infect Dis 2017;64:902-911.
  2. Arduino MJ. Tap water avoidance decreases rates of hospital-onset pulmonary nontuberculous Mycobacteria — a call for water management in healthcare. Clin Infect Dis 2020; Aug. 23. doi:10.1093/cid/ciaa1242. [Online ahead of print].