Factors associated with the isolation of Nontuberculous mycobacteria (NTM) from a large municipal water system in Brisbane, Australia

Our plain-English summary of Factors associated with the isolation of Nontuberculous mycobacteria (NTM) from a large municipal water system in Brisbane, Australia, by R.M. Thomson, R. Carter, C. Tolson, et al (BMC Microbiology, 2013).

The study

• Authors: R.M. Thomson, R. Carter, C. Tolson, C. Coulter, F. Huygens, M. Hargreaves
• Journal: BMC Microbiology
• Published: 2013;13:89
• Cited by: 89 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Nontuberculous mycobacteria (NTM) are normal inhabitants of a variety of environmental reservoirs including natural and municipal water. The aim of this study was to document the variety of species of NTM in potable water in Brisbane, QLD, with a specific interest in the main pathogens responsible for disease in this region and to explore factors associated with the isolation of NTM. One-litre water samples were collected from 189 routine collection sites in summer and 195 sites in winter. Samples were split, with half decontaminated with CPC 0.005%, then concentrated by filtration and cultured on 7H11 plates in MGIT tubes (winter only).

Results: Mycobacteria were grown from 40.21% sites in Summer (76/189) and 82.05% sites in winter (160/195). The winter samples yielded the greatest number and variety of mycobacteria as there was a high degree of subculture overgrowth and contamination in summer. Of those samples that did yield mycobacteria in summer, the variety of species differed from those isolated in winter. The inclusion of liquid media increased the yield for some species of NTM. Species that have been documented to cause disease in humans residing in Brisbane that were also found in water include M. gordonae, M. kansasii, M. abscessus, M. chelonae, M. fortuitum complex, M. intracellulare, M. avium complex, M. flavescens, M. interjectum, M. lentiflavum, M. mucogenicum, M. simiae, M. szulgai, M. terrae. M. kansasii was frequently isolated, but M. avium and M. intracellulare (the main pathogens responsible for disease is QLD) were isolated infrequently. Distance of sampling site from treatment plant in summer was associated with isolation of NTM. Pathogenic NTM (defined as those known to cause disease in QLD) were more likely to be identified from sites with narrower diameter pipes, predominantly distribution sample points, and from sites with asbestos cement or modified PVC pipes.

Conclusions: NTM responsible for human disease can be found in large urban water distribution systems in Australia. Based on our findings, additional point chlorination, maintenance of more constant pressure gradients in the system, and the utilisation of particular pipe materials should be considered.

In plain English

This study tested Brisbane's public drinking water for nontuberculous mycobacteria (NTM), bacteria that can cause lung disease. Asbestos appears only as one of the water pipe materials compared. The study did not measure asbestos fibers or any asbestos-related disease. One-litre samples were taken from 195 sites in winter (July-August 2007) and 189 sites in summer (December 2007-January 2008). Mycobacteria grew from 82.1% of sites in winter (160/195) and 40.2% in summer (76/189). The authors attributed the lower summer yield to contamination. Whether a site grew NTM at all did not differ significantly by pipe material. Species known to cause disease in Queensland were more likely to come from sites with narrower pipes, mostly distribution points, and from asbestos cement or modified PVC pipes. For asbestos cement pipes, the article's table counted 91 pathogenic and 55 non-pathogenic NTM. The p value of 0.046 compared all pipe materials together, not asbestos cement alone. The authors noted that some pipe-material groups were too small to be statistically meaningful, and that they could not assess disinfectant or nutrient levels. They suggested considering extra chlorination, steadier pressure and particular pipe materials.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Environmental sampling study of a municipal drinking water distribution system, with samples taken in two seasons and cultured for mycobacteria
• Who was studied: One-litre water samples from routine water-quality sampling sites in Brisbane, Australia: 189 sites in summer (December 2007-January 2008) and 195 sites in winter (July-August 2007), out of 217 sites in total. The sites were distribution points, reservoirs and trunk mains.
• Exposure: Features of each sampling site compared against culture results: pipe material (including asbestos cement, cement-lined iron or steel, cast iron, PVC and others), pipe diameter, mains age, distance from the nearest reservoir and from the treatment plant, and elevation. No asbestos fiber exposure or human exposure was studied.
• Main results:
  • Mycobacteria were grown from 40.2% of sites in summer (76/189) and 82.1% of sites in winter (160/195).
  • Whether a site grew NTM did not differ significantly by sample type, mains age, pipe material or distance from the nearest reservoir.
  • Sites with asbestos cement pipes: 28 (30.8%) were NTM negative and 63 (69.2%) were NTM positive. The overall p value for the comparison across pipe materials was 0.166 (not statistically significant).
  • Pathogenic NTM were more likely to be found at sites with narrower diameter pipes (mostly distribution points) and at sites with asbestos cement or modified PVC pipes.
  • For asbestos cement pipes, the table lists 91 (62.3%) pathogenic and 55 (37.7%) non-pathogenic NTM. The p value of 0.046 applies to the comparison across all pipe-material categories, not to asbestos cement alone.
  • Mean pipe diameter was 360.82 mm (SD 414.90) where pathogenic NTM were found and 509.74 mm (SD 503.47) where non-pathogenic NTM were found (p less than 0.0001).
  • For sites supplied by the Mt Crosby plant in summer, mean distance from the treatment plant was 85.40 km for NTM-positive sites, 82.50 km for contaminated or overgrown sites and 81.75 km for negative sites (p = 0.015). In winter the distances were similar (p = 0.581).
  • M. kansasii was frequently isolated. M. avium and M. intracellulare, described as the main disease-causing species in Queensland, were isolated infrequently.
• The authors' conclusion: The authors concluded that NTM species that cause human disease are present in the drinking water system of a major Australian city. Based on their findings, they suggested that additional point chlorination, more constant pressure gradients and the use of particular pipe materials should be considered.
• Limitations the authors state:
  • Some pipe-material categories had too few sites to be statistically meaningful.
  • The authors could not assess the role of disinfectant concentrations or nutrient levels.
  • Contamination lowered the summer yield.
  • Liquid culture media (MGIT tubes) were used only in winter.
  • Concentrations of individual NTM species were not measured.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement.

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