Designing for healthy hospital water systems
Plumbing Connection teams up with Enware to discuss how you can help prevent legionellosis by making sure that the water systems in buildings are maintained.
Since the first documented outbreak of Legionellosis in Philadelphia in 1976, more than 42 Legionella species have been identified. Hospitals are one of the highest risk environments for Legionella as they have large and complex water systems that are difficult to monitor, filter, temper and flush. Couple this with the vulnerability of those using the systems and the threat of Legionella in hospitals intensifies.
So what exactly is Legionella and what measures can we take to prevent it spreading?
Legionella bacteria occur everywhere in lakes and rivers, although the concentration of Legionella in natural habitats is low. Elevated temperature, inorganic and organic contents of the water and the presence of biofilm play key roles in its growth and spread. These factors may explain why Legionella increases in density in artificial habitats such as man-made warm water systems. The disease causing bacteria start to multiply in water at temperatures over 20°C with the highest concentrations found in water samples of 30-40°C. Optimum conditions for Legionella growth are found in warm stagnant water reaching a temperature of around 35°C.
While the Legionella bacteria is commonly portrayed as rare, scientific research has shown that this is not the case. Research by the Centres for Disease Control and Prevention (CDC) found that 70% of hospitals tested had Legionella bacteria in their water systems.
Legionnaire’s disease – Transmission and recent outbreaks
The diseases caused by Legionella are collectively termed Legionellosis. Legionnaires’ disease is the pneumonic form of Legionellosis, while the benign flu-like form is called Pontiac fever. Legionnaires disease has an incubation period of 2-10 days and begins with a mild cough, malaise, muscle aches, low fever and gastro-intestinal symptoms. Later symptoms include high fever, alveolitis, kidney failure, diarrhoea and bronchiolitis.
Legionellosis is transmitted by breathing in fine droplets of water that contain the bacteria. It can’t be transmitted person to person or by drinking contaminated water.
A significant outbreak of Legionnaire’s disease occurred in February 2015 in New York, resulting in the death of 12 people with at least 100 others infected.
In the UK, clinical studies have shown that Legionnaires accounts for around 3% of the 200,000 cases of community acquired pneumonia’s diagnosed each year. This means that the actual number of cases occurring may be over 10 times higher than the number of reported cases and could be more than 5000 cases per annum. Additionally, worldwide incidences of hospital-acquired Legionnaires disease are increasing.
While effective antimicrobial treatment is available, this is often complicated by underlying diseases or misdiagnosis. This contributes to the much higher mortality rate of 33% for hospital acquired Legionnaires disease, compared to 13% for community acquired cases of the disease.
Closer to home, one of Australia’s biggest outbreaks occurred in 2013, when contaminated warm water drawn through hospital taps at Brisbane’s Wesley Hospital resulted in the death of a patient and left another critically ill in intensive care.It was reported that a State Government energy efficiency program may have increased the risk of Legionella bacteria growing in water supplies.
Temperature controls in place at the hospital meant water could not reach a temperature higher than 45°C. This created an optimum environment for bacteria growth.
Legionella and hospital water systems
During a recent study of eight hospitals in the US and Spain, 100% of hospital water systems colonised with Legionella reported hospital acquired Legionnaires disease, which was uncovered following subsequent clinical surveillance.
In a US National surveillance study of 20 hospitals, 14 were found to have water systems colonised with Legionella, with six of the 14 reporting high levels of contamination. Of the six hospitals, four discovered cases of hospital acquired Legionnaires’ disease.
Stagnation is another key breeding factor that will exacerbate Legionella growth in water systems. When water is used infrequently or where there are significant dead legs in pipework, the risk of contamination is increased. It is both good design practice and the requirement of various State Health guidelines to reduce the length of warm water pipework in order to minimise dead legs, and in some circumstances to remove them completely as well as ensuring systems are flushed on a weekly basis when taps have not been in use.
Legionellae in cold water systems
While warm water systems have historically been the cause of many outbreaks of Legionella, due to their optimum temperature for bacteria growth, over the last few years Legionella bacteria have increasingly been discovered in cold water systems. This is due in part to energy conservation measures, particularly improved insulation in new buildings, which promotes better heat retention and reduces energy losses.
Cold water distribution systems are a natural heat shield in buildings due to the temperature difference between the system and the ambient air. As a consequence the water within these systems becomes increasingly warm, rising to a temperature which supports the proliferation of Legionella bacteria.
A study of four healthcare facilities in Germany with cases of healthcare associated Legionnaires disease, found cold water samples taken from distal sites were more frequently contaminated (40% vs. 23%) and contained higher concentrations of Legionella than warm water samples.
This is despite only 5% of the cold water samples displaying a temperature of over 25°C (the temperature at which Legionellae multiply) at sampling time.
This may be due to the “warming up” effect of cold water, which can occur after long periods of inactivity or when the cold and warm water pipes are closely fitted in the same shaft without appropriate insulation. This warming up effect may not be detectable at the time of sampling, but highlights the importance of regular assessment of cold water systems.
Water movement and preventing stagnation
Regular movement of cold water around the distribution system, and as close to the outlets as possible is necessary to reduce the build-up of biofilm by preventing stagnation. This also helps to keep temperatures low, slowing Legionella growth.
Additionally, the increased force caused by regular movement can help prevent excessive biofilm from accumulating in the distribution pipes.
Designers, plumbers and healthcare professionals need to consider the risk of waterborne infection arising from the installation of excessive numbers of outlets.
Cold water distribution pipework and storage tanks in new healthcare premises are frequently oversized and it is common practice to fit more tap and shower outlets than are needed. If outlets are not used regularly the cold water within the distribution pipes and associated cold water storage tanks can become stagnant, and water temperatures can rise into the temperature zone that supports the growth of biofilm and the proliferation of Legionella bacteria.
The Plumbing Code of Australia (NCC Volume 3 – 2015) requires heated water be stored and delivered under conditions which avoid the likelihood of the growth of Legionella bacteria. The National Plumbing and Drainage Code stipulate hot water be stored at no less than 60°C to help prevent the growth of Legionella.
However these temperatures can cause scalding, so water temperature is required to be controlled in accordance with AS/NZS3500.4. This standard currently states that in healthcare facilities the only deemed-to-satisfy solution is through the use of thermostatic mixing valves set to a maximum temperature of 45°C.
What can go wrong?
In the case of Brisbane’s Wesley Hospital, managing the outbreak was not easy. A full scale public health unit investigation into the hospital’s cooling and water systems, as well as independent sampling and investigations, found the source of contamination was the heated water system.
Contributory factors to the harbourage of Legionella were identified in the presence of dead legs, and a lack of awareness regarding the need for regular and on-going maintenance of plumbing fittings. Following the incident, Queensland Health asked almost 250 state and private hospitals to test their water systems for Legionella. The results indicated the extent of Legionella in water systems, with at least a quarter of all hospitals tested returning a positive result.
Benchmarking hydraulic design
While internal water systems in Australia have traditionally been designed with issues such as Legionella control in mind, inconsistency differences between the minimal design guidelines of the various States and other regulatory bodies’ means conflicts can occur. The ongoing threat of Legionnaire’s Disease is a very real one and therefore something must be addressed by the building, design and plumbing sectors.
Thankfully we are blessed with hindsight and can look to European models that are leading the way in the management of Legionella in hospitals. The UK Department of Health provides comprehensive advice and guidance in a code of practice for the control of Legionella in health water systems, namely the temperatures at which water should be maintained at throughout a hospital’s water supply system.
These practices are focussed around distributing water hot at all times therefore requiring a thermostatic mixing valve for safe warm water delivery avoiding potential scalding risks. Ideally for safe water delivery and to minimise microbial growth risks in plumbing systems, thermostatic mixing valves which mix hot and cold water at the point of use should be used. By integrating the thermostatic mixer into a point-of-use mixer, the risk of Legionella is minimised as full temperature heated water is plumbed directly to the draw off fixture eliminating warm water pipe lines where Legionella may breed.
What can be done
A number of measures can be employed to control Legionella bacteria in hot and cold potable water systems.
- High and Low temperatures (>50 at hot water distribution outlets (>50 at hot water distribution outlets and <20 at cold water outlets.
- Anti-bacterial water treatment regimes (Chlorine dioxide, copper and silver ions, silver and hydrogen perozide, UV, ozone etc).
- Regular flushing of outlets, or purging of them immediately prior to use – without generating aerosols.
- Point of use filtration.
- Regular monitoring of the water distribution system. Legionella site positivity and control measures need to be routinely monitored for the life of the system.
- Water storage should be kept to the safest minimum.
- Water velocities within the pipes should be increased for improved water movement.
- All pipework should be lagged and wherever possible, cold pipes separated from heat sources.
- For safe delivery, thermostatic mixing valves which mix hot and cold water at the point of use should be used to ensure the water can be kept hot for as long as possible without the risk of scalding.