Stephen Flatman, Author at Harper Water

Stephen Flatman

Legionella, Pseudomonas aeruginosa and NTM (non-tuberculous mycobacteria) in household showers: Should we take note?

Do Legionella, Pseudomonas aeruginosa and non-tuberculous mycobacteria in household showers occur and, if yes, do they play any role in consumers’ health? We know that Legionella is a waterborne pathogen (bacterium) known to cause lung infections. The severity and impact of legionellosis can vary from mild illness (Pontiac fever) to a potentially fatal form of pneumonia (Legionnaires’ Disease).It is also well known to be transmitted through aerosols created by cooling towers, air conditioning systems, and water system outlets such as taps and showers within households and premises, and that inhalation of aerosols contaminated with Legionella can lead to infection1. Typically the perception (and therefore focus of attention) is on these instances occurring outside of the home.  What is less recognised, is the significance within household water applications, where showers2,3 have been ranked the second highest in a relative ranking of Legionella exposure pathways after ultrasonic and cool mist humidifiers4. Inhalation of water aerosols containing Legionellae, Pseudomonas aeruginosa or non-tuberculous mycobacteria during routine domestic household showering has been implicated in life-threatening respiratory infections for immunocompromised individuals5-7. Legionella can live and thrive in water (or within an attached biofilm) of complex water systems as well as inside amoeba – their natural host8. Schoen & Ashbolt described a sequencing model showing how the Legionella that lives and multiplies within water biofilms, becomes detached from the biofilm during showering, before then being transported and aerosolized at the showerhead. Finally it shows how it is then inhaled by humans and deposited in the alveolar region of the lungs9. The concentration and release of any created aerosols into the environment, becomes therefore critical for any showerhead user (regardless of the type of premises), especially given that opportunistic pathogens can be capable of causing serious and life-threatening infections in severely immunocompromised individuals10. A number of factors influence the size and concentration of aerosols created by a showerhead, these include; ambient humidity, type of shower install, design of the showerhead, water temperature, piping materials, the users or the bacterial communities and biofilm development11.  As far as we know, and in terms of how showerhead design works in practice, low-water consumption showerheads have been shown to generate a significantly higher number of aerosols (due to smaller internal bore size and higher pressure) compared to that of standard showerheads12. In 2009, Feazel et al. sampled 45 showerhead surfaces from 9 cities in the US and showed that these biofilms were enriched with > 100-fold above background water content of mycobacteria, especially M. avium and M. gordonae5. In the UK in 2017, Collins et al. investigated the occurrence of Legionella spp. in UK household showers. Out of the 99 household showers sampled in the South of England, 8 % of the shower water sampled tested positive by culture for clinically relevant Legionella spp, with a 31 % incidence of positive results obtained via qPCR (quantitative Polymerase Chain Reaction, a culture-independent diagnostics method)13. The authors clearly state, therefore, how household showers may be important reservoirs of Legionella and should be considered in source investigations13. To summarise, controlling the water quality within an in-premise water system, by cleaning, disinfecting and/or exchanging shower hoses and shower heads regularly, whilst avoiding stagnation caused by underuse of water, are some of the measures that can be employed to help minimise the risk of pathogen-contaminated aerosol release during the showering process and the inherent risks that can result. To discuss this further, or if you wish to learn more on this and other related topics, please do not hesitate to contact the team directly at 1. Casini et al., J Hosp Infect, 69(2), 141-147, 2008 2. Cowen & Ollison, J of the Air & Waste Management Association, 56(12), 1662-1668, 2006 3. Schoen & Ashbolt, Water Research 45:5826-5836, 2011 4. Hines et al., Water Res, 56, 203-13, 2014 5. Feazel et al., Prot Natl Acad Sci, 106(38), 16393, 2009 6. Perinel et al., Int J Hyg Environ Health, 221(2), 252-259, 2018 7. Proctor et al., Environ Sci: Water Res Technol, 2(4), 670-682, 2016 8. Lau & Ashbolt, J Applied Microbiology, 107(2), 268-278, 2009 9. Schoen & Ashbolt, Water Research 45, 5826-5836, 2011 10. Perkins et al., Appl. Environ. Microbiol. 75, 5363-72, 2009 11. Allegra et al., Water Research 172, 115496, 2020 12. Estrada-Perez et al., Water Research, 130, 47-57, 2018 13. Collins et al., Int J Hyg Environ Health, 220, 401-6, 2017

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Legionella in private homes: Can they cause infections?

In the last 20 years many reports have been published about private homes’ water systems being contaminated with Legionella, with hot water temperature being probably the most important factor for Legionella multiplication (Hayes-Philipps, 2019). In a German study, 12 % of 452 samples taken from private homes was contaminated with Legionella, with maximum counts of < 100,000 cfu/100 ml (Mathys et al., 2008). A further study from Australia found that 74 % and 64 % of tested domestic showers presented positive for Legionella spp. and Legionella pneumophila respectively (Hayes-Philipps, 2019). The German Robert Koch-Institute, German Health Authorities and the Reference Laboratory for Legionella carried out the German‚ LeTriWa‘ study in Berlin from 2016 to 2019 with impressive results. 111 study cases and 202 controls have been included in this study. In order to establish the private homes’ water system as a possible source of Legionella infections, microbiological evidence has been gathered (inclusion of a MAb 3/1-positive strain). In 25 % of the study cases the water system within the private residencies was identified as the source of Legionella infections (Buchholz et al., 2020). Samples were taken from bathrooms in each household and included a pre flush, post flush and biofilm swab from the tap outlets. In addition, pre flush and biofilm swab samples were taken from the shower outlets. The results demonstrated microbiological evidence of the residential drinking water acting as the source of infection in 24 of the 111 study cases. A further 5 cases from the 111 included within this study pointed firmly towards the drinking water within these private residences as the infection source based on cluster evidence (Buchholz et al., 2020).  In total, the authors highlighted how half of the cases of Legionella infection were likely to have arisen from the residential drinking water as the primary source of infection (Buchholz et al., 2020), whilst concluding that Legionnaires’ Disease seems to be conferred primarily by the type of Legionella rather than the amount (Buchholz et al., 2020). More recently a private building’s drinking water system was implicated as the source of Legionella infection within Italy, with two confirmed Legionnaires’ Disease cases, one of which proved fatal (Ricci et al., 2021). Water samples that were taken from the building and the apartments of the 2 diseased tenants have been found to be positive for Legionella pneumophila with counts between 100 and 1400 cfu/100 ml (Ricci et al., 2021). The respective risk assessment carried out for this private building confirmed warm water temperatures between 45 and 56 °C being a critical factor (Ricci et al., 2021). Appropriate risk assessments for private buildings and apartment buildings have been suggested in literature and guidance (HSE HSG274 Part 2, 2014) and there are countries, where a regular testing for Legionella is mandatory (German Drinking Water Ordinance). This is especially relevant to immunocompromised and elderly people as they are more susceptible to Legionella infections. Home showers and taps should be checked more frequently in general and especially where tenants are immunocompromised or older (Ricci et al., 2021, Hayes-Philipps, 2019). It is widely acknowledged that many cases of unreported Legionnaires’ Disease across all sectors and spanning all geographies are likely being missed. With increasing focus on private homes given demographic changes, and a growing body of evidence beginning to emerge, it seems reasonable to assume that the similar risk factors we have learned so much about in recent years across the healthcare industry in particular, can also be considered highly relevant to domestic homes and properties. Literature Buchholz et al., „Source attribution of community-acquired cases of Legionnaires’ disease – results from the German LeTriWa study; Berlin 2016-2019″, PLoS ONE 15(11):e0241724, 2020 Mathys et al., „Occurrence of Legionella in hot water systems of single-family residences in suburbs of two German cities with special reference to solar and district heating“, Int. J. Hyg. Environ. Health 211, 179–185, 2008 German Drinking Water Ordinance accessed June 2021 Ricci et al., „A Legionnaires’ Disease Cluster in a private building in Italy, Int. J. Environ. Res. Public Health, 18(13),6922, 2021 Hayes-Philipps et al., „Factors influencing Legionella Contamination of domestic household showers“, Pathogens, 8(1), 27, 2019 Health and Safety Executive HSE „Legionnaires’ Disease. Part 2: The control of Legionella bacteria in hot and cold water systems“, HSG274 Part 2, 2014

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Re-opening your building & Water Safety Planning?

As we enter this critical ramp up phase in preparation and planning, how robust is your water safety planning, and how confident are you with the suitability of your risk assessment and pre-pandemic maintenance provisions? The unforeseen and unintended consequences of COVID 19 lockdowns have presented a number of scenarios not seen before and have brought about further challenges to building water management.  From the 12th of April, 2021 many sections of industry have begun to reopen, and in the next phase of re-opening in England, scheduled for the 17th of May, 2021, we will see many more service providers open their doors once more. Are you about to recommission and re-open your building facilities or bring your water system back into use after unprecedented periods of extended under-use, as a result of national COVID lockdown?  During preparations to re-open, have you thought about your water systems maintenance and the risks to user’s health? If you are the Duty Holder or Competent Person responsible for the building, then please consider reviewing the Health & Safety Executive (HSE) guidance on post-pandemic building reopening including water safety planning. Based on HSE guidance, Risk Assessments (RA) should be updated to include the stagnation period during lockdown.  A lack of water turnover and flow, plus any compromise to temperature control resulting from stagnation are proven to be major contributing factors to Legionella (and other waterborne pathogens) growth, leading to an elevated risk of system-wide contamination. Buildings that have been closed for several months are highly susceptible to such contamination, unless regular flushing regimes have been in place and correct temperatures maintained throughout the lockdown. The HSE recommends that you review your RA to manage Legionella risks when you a) reinstate your water system or start using it again and b) restart some types of air conditioning units. For detailed information, please see; Furthermore, the HSE advises building managers to work with competent consultants to accompany you with your reopening actions required on building water systems. Harper Water Management Group is ideally positioned to provide professional support and advice, and partner with you and your team(s) in reviewing and updating your current RA, auditing, and advising on critical actions required to ensure safety and compliance for the re-opening and returning of your system to full usage. For further information and advice, please do not hesitate to contact our IHEEM Registered Authorising Engineer and educational team at

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