WATER SYSTEM HYGIENE AND SAFETY
cleaned. The anti-scald design involves mixing hot and cold water, which can create the ideal water temperature for Legionella multiplication. Also, the inner design of these units is complex, and can harbour pockets of stagnant water, encouraging biofilm growth, which is difficult to remove.
A ‘never-ending battle’ It is true to say that Legionella is a never-ending battle. It is persistent and difficult to eradicate, and ultimately it can be deadly, so the management of Legionella in hospitals is critical. Hospital management shouldn’t see Legionella control as an ‘add-on’ to the day job, but as an imperative element of patient safety and care standards. Preventive measures may include maintaining appropriate temperature and pressure levels, regular cleaning and disinfection of water systems, and regular flushing to avoid stagnation, together with ongoing testing to detect Legionella presence. It is a well-documented fact
that one of the major risk factors for Legionella proliferation within a water system is temperature.9,10
Biofilm on a tap spout – a major indicator for Legionella risk. The ideal
temperature range which encourages the growth of Legionella bacteria is 20 °C to 45 °C (77-113 °F). Legionella isn’t a fan of temperature extremes, so creating a hostile environment by keeping cold water cold (below 20 °C), and hot water hot (above 60 °C in storage tanks, and above 50°C in the circulating system), is a simple yet effective step in helping reduce risk, and should be a minimal-level method of Legionella control in any water management process.
Disinfection Disinfection has also proven itself to greatly reduce waterborne infections, and is one of the greatest advances in the prevention of disease in the last century, and maintaining levels within a water system will help keep Legionella in check. However, disinfectant presence in water systems can also conversely encourage the growth of OPPPs (Opportunistic Premise Plumbing Pathogens) like Legionella pneumophila. As disinfectant reduces the number of pathogens in the water, it also reduces the number of competitors for the available carbon and nutrients. Ironically, this can give OPPPs an increased opportunity to proliferate.11 Regular cleaning might involve the
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identification and removal of the biofilm which can be found in most water systems – natural and man-made, throughout the entire world. Biofilm is very common, and if you look inside taps, showerheads, pipework, or water tanks, you are likely to find biofilm residing within. It is widely considered that a majority of Legionella is locked in biofilm, and issues occur when sections of biofilm break off, leading to the release of the bacteria into the water, where they can clog up filters or deadlegs, and embark on their relentless journey to infect the whole water system. Biofilms also provide Legionella with protection from high temperatures in the water or chemical treatments, allowing them to proliferate into larger and more dangerous quantities uninterrupted.
A dormant state It is really important to note, however, that when Legionella is exposed to stressful conditions such as starvation, chemical treatment (e.g. chlorination), heat shock treatments, low temperatures, and UV treatment, it can enter a dormant state called VBNC (Viable but Non-Culturable) Legionella. This dormant state suggests an adaptive strategy for the long-term survival of the bacteria under unfavourable
Disinfection has also proven itself to greatly reduce waterborne infections, and is one of the greatest advances in the prevention of disease in the last century, and maintaining levels within a water system will help keep Legionella in check
48 Health Estate Journal May 2023
environmental conditions, and as the name suggests, it cannot grow on conventional culture plates in a laboratory. It will therefore remain undetected if water testing programmes only rely on lab culture, as many healthcare settings do. When conditions become favourable again, VBNC Legionella may reactivate. VBNC Legionella is very dangerous, and has been shown to retain pathogenic properties despite restricted metabolic rates.12
It has been observed that VBNC
bacteria have recovered their culturability after passage through human lung cells, which they can directly infect, suggesting that after VBNC bacteria are inhaled by a human, they have the potential to cause infection in the same way as culturable bacteria.13
It is clear that hospitals take
grave risks when they only use lab culture methods to check their water systems for Legionella.
Hiding within the system So, if a hospital finds Legionella, and takes steps to remove it, only to find that the bacteria is back again, it could be that VBNC Legionella is hiding within the system. Undertaking a test that can detect VBNC forms of the bacteria (e.g. antibody-based lateral flow tests or PCR) after all remedial work is critical to ensure efficacy. The only way to know if culturable and
VBNC Legionella is present in the water is to test it regularly. There are options available on the market to support a regular testing regime. Lab culture is considered the traditional method, and is required by many Legionella codes of practice, including the Department of
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