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Non-Tuberculous Mycobacteria Shared Learnings

The Harper Water team are active within Project Water Safety Groups in several new build and refurbishment projects impacting high risk patient groups such as adult and neonatal intensive care, oncology and transplant.  These projects have enabled broader Non-Tuberculous Mycobacteria (NTM) learning and experience to best support engineering, microbiology and hygiene measures.  Understanding NTM prevalence in healthcare waters, and recognising this source of infection and the potential transmission routes are critical to enabling appropriate risk elimination and mitigation.

Key points to take into consideration with NTM and water systems

  • In-premise plumbing is an ideal habitat for NTM with lots of surface area and plenty of niche for NTM colonisation and biofilm formation.
  • NTM is highly resistant to temperatures, low oxygen levels seen with stagnancy and disinfectants.  Therefore, traditional primary and secondary control measures are ineffective.  NTM also thrive in low nutrient environments (e.g. distilled or reverse osmosis waters) and survive extended periods of desiccation.  Draining and “drying” will not deter this organism.
  • Transmission in the form of NTM-laden aerosols generated from showers or running a tap, dust-inhalation (construction), direct skin contact with contaminated waters particularly those with skin lesions, undergoing surgery, having intravascular catheters and cardiopulmonary bypass.  Additionally skin infections are reported after tattooing or cosmetic practices with intradermal or subcutaneous injections.  Risk should be recognised in individuals with gastroesophageal reflux disease (GERD), a poor swallow reflex (elderly or stroke affected), or those drinking whilst prone due to aspiration of NTM contaminated fluids
  • Patient risk factors include age (> 60 years old), gender (more likely female), exposure to contaminated in-premise water system, occupation (farmers), existing lung disease or deficiency, existing immune disease or deficiency.  The main NTM species causing human infections are slowly growing species, such as Mycobacterium avium or M. kansasii, and rapidly growing ones, such as M. abscessus or M. chelonae.

To proactively consider at the design and specification stage

  • Reduce surface areas available for colonisation –ensure simple design, remove long legs, no aerators, risk assess and reduce presence of shower heads, thermostatic mixing valves or other complex componentry, avoid rubber and plastic materials
  • Reduce the number of outlets.  Risk assess if a water service is needed, this will enable increased turnover of water at the periphery through fewer water services and reduce peripheral water stagnancy.  If an outlet is predictably low use (e.g. not used daily) such as showers, thorough flushing regimens or automatic flushing componentry should be implemented.  It is important to recognise that flushing is to reduce the stagnant conditions and low oxygen waters that NTM (and other organisms) can thrive in

Prof Joe Falkinham has had an extensive career with NTM, pioneering much of the research, data and knowledge we have to date, and therefore his publications are the bedrock for any risk recognition and assessments.  With increasing problems encountered with NTM disease, we are also seeing more frequent publications, and this blog shares 3 recent papers which add helpful information and evidence for Water Safety Groups

Yu et al., highlight that in-premise water systems present a significant NTM health risk to occupants.  The team sampled water, biofilm and sediment from multiple locations within 23 high-rise building in-premise water systems which used chloramine as a secondary systemic biocide.  NTM colonisation has been found to be worse in the top levels of multi-floor buildings and chloramine may have limited effectiveness in controlling NTM and possibly encouraging growth (Stanish et al., 2016; Waak et al., 2019). 

The team found in-premise NTM numbers were 100 times higher than in the distribution system, with a distinct set of communities highlighting the adaptability of NTM populations to different environments and challenges.  As expected, there were higher densities of NTM in the biofilms than the water phase, but also greater diversity illustrating the persistence and protective effect of the biofilm blanket.  There were also differences between material types, with NTM favouring growth with plastics and rubbers.

A paper from the French NTM Reference Laboratory in Paris (Allam et al), shares their standardised protocol for detection and quantification of NTM in tap water, but also the application of this protocol in investigating healthcare acquired infections and identifying the source of contamination in order to prevent new infections.  Culture is challenging with regards to recovering NTM from the complex environmental flora found in a water sample.  This team developed and used their protocol to investigate environmental sources of clinical NTM infection over a period of 10 years (2014-2024).  NTM were detected in water samples in 92% of investigations into clinical cases, with approximately half revealing the same NTM species in clinical and environmental samples with close genomic profiling.  Water samples associated with infections were taken from mesotherapy, seawater swimming pool, tattoo ink, patient home water supply, hospital heater-cooler units, hospital potable water (showers and basins), and a mobile spa bath in a nursing home.

It is clear with the use of whole genome sequencing that there is a link between environmental presence and clinical cases of same strain NTM.  With NTM infections emerging as a growing problem, reliable investigation of sources will be critical to eliminating or mitigating against further disease.

The excellent civil engineering and microbiology teams from Montreal, Canada (Grimard-Conea et al), have published their experiences of long term (> 12 months) onsite biocide (monochloramine) water treatment on Legionella pneumophila, NTM, Vermamoeba vermiformis and physico-chemical water quality within a hospital hot water system.

Measuring efficacy of biocide treatments is not straightforward due to impacts of water system design, materials, temperatures and user behaviours (throughput).  However, this team used an innovative sampling approach to assess 22 distal sites at tap and shower outlets and compared them to 10 control points within the main body of the hot water system which included the calorifiers and individual return loops.

Monochloramine successfully reduced culturable Legionella pneumophila populations by up to 3 logs within a period of 24 hours, and utilising genetic testing reported a reduction in gene copies within 4 weeks.  There was less impact on Vermamoeba vermiformis and NTM levels appeared stable.   In order to achieve this level of performance, monochloramine concentrations of 2-3 mg/L were required alongside hot water temperatures greater than 55 oC.  This biocide concentration and temperature control was only consistently maintained within the main body of the hot water system, with the distal sites unable to sustain.  A period of interruption to monochloramine dosage led to significant rebound growth in all the microbiological organisms monitored, highlighting their continued presence and persistence within biofilms.  Copper and lead release was reported with concentrations rising 1.8 and 4.6 fold respectively, illustrating the corrosive impacts of biocide on the system fittings and infrastructure.

This study highlights important factors to consider and monitor when determining efficacy of any systemic biocide treatments, and the critical nature of ensuring good hot water circulation and flow through hydraulic balance, no presence of dead legs, adequate throughput at all outlets, consistently maintained hot water temperatures at a minimum of 55 oC, and to recognise that the persistence of biofilms within a water system will support rapid rebound growth given any lapse in control measure performance.  It is an excellent document to support Water Safety Groups evaluate their secondary biocide treatments if they are already being used or where being considered as part of an holistic approach to waterborne pathogen control.

We hope these papers are of interest to Water Safety Groups, Capital Project teams and wider in-premise water hygiene supporters.  If you would like to discuss any aspects of these papers or relevant new design or refurbishment projects, please contact us.

References:

  • Allam C, Haenn S, Giraud E, Awad Z, Robert J, Cambau E, Moulin L, Mougari F. Standardised protocol for the detection and quantification of nontuberculous mycobacteria (NTM) in tap water and its application in investigating the source of NTM clinical infections. Int J Hyg Environ Health. 2025 Jul;268:114618. doi: 10.1016/j.ijheh.2025.114618. Epub 2025 Jul 8. PMID: 40633228.
  • Falkinham JO 3rd. Ecology of Nontuberculous Mycobacteria. Microorganisms. 2021 Oct 30;9(11):2262. doi: 10.3390/microorganisms9112262. PMID: 34835388; PMCID: PMC8625734.
  • Falkinham JO 3rd. Nontuberculous mycobacteria in the environment. Tuberculosis (Edinb). 2022 Dec;137:102267. doi: 10.1016/j.tube.2022.102267. Epub 2022 Sep 28. PMID: 36191391.
  • Grimard-Conea M, Marchand-Senécal X, Faucher SP, Prévost M. Mitigation of opportunistic drinking water pathogens by onsite monochloramine disinfection in a hospital water system. Water Res. 2025 Jun 25;285:124107. doi: 10.1016/j.watres.2025.124107. Epub ahead of print. PMID: 40591989.
  • Shi X, Ying R, Sha W. Correlation between Water Environment and Prevalence of Nontuberculous Mycobacteria Pulmonary Disease: A Case-Control Study. Altern Ther Health Med. 2024 Sep;30(9):172-177. PMID: 38064622.
  • Stanish LF, Hull NM, Robertson CE, Harris JK, Stevens MJ, Spear JR, Pace NR. Factors Influencing Bacterial Diversity and Community Composition in Municipal Drinking Waters in the Ohio River Basin, USA. PLoS One. 2016 Jun 30;11(6):e0157966. doi: 10.1371/journal.pone.0157966. PMID: 27362708; PMCID: PMC4928833.
  • Waak MB, Hozalski RM, Hallé C, LaPara TM. Comparison of the microbiomes of two drinking water distribution systems-with and without residual chloramine disinfection. Microbiome. 2019 Jun 7;7(1):87. doi: 10.1186/s40168-019-0707-5. PMID: 31174608; PMCID: PMC6556008.
  • Yu W, Yang J, Cai X, Xia S, Wang H. Unraveling the Dynamics and Growth Potential of Non-Tuberculous Mycobacteria along Water Transportation in Chloraminated Secondary Water Supply Systems. Environ Pollut. 2025 Jul 10:126812. doi: 10.1016/j.envpol.2025.126812. Epub ahead of print. PMID: 40651654.