Dr Susanne Surman-Lee provided a review, strategies and guidelines for preventing contamination of water systems. She has been appointed co-chair of the International Forum for Water Hygiene in Buildings, has input into various standards for Legionella and is an author/editor of the WHO guidelines on ‘Water Safety in Buildings’.
Dr Surman-Lee noted that water systems are recognised sources of infections and explained the WHO definition as ‘hazard’ while the potential for causing harm is ‘risk.’ Routes of infection might be through drinking contaminated tap or bottled water, via ingestion from food prepared using contaminated water, or use of a pool or spa pool with high levels of contaminating microorganisms.
Cryptosporidium parvum for example, has cysts which are very resistant to chlorine and can cause severe diarrhoea. Giardia, a similar type of protozoan, also causes unpleasant digestive symptoms lasting up to six weeks.
Dr Lee advised that the potential hazards must be identified. “Good quality source water is essential but this may still need treatment on entering a building, perhaps filtration, maybe combined with UV or other treatments. A systematic multidisciplinary brainstorming approach is essential as well as a contingency plan in case of any disruption to the water system.”
These organisms grow naturally in water and on surfaces of components and pipework , particularly in association with biofilms. These fine layers of organisms, which attach very strongly to surfaces, sediments and particulates in water systems, are very problematic to control and may survive water treatment.
Pseudomonas aeruginosa is a leading cause of waterborne disease, occurs widely in nature and is highly tolerant of a variety of physical conditions including some biocides. The risk factors for Pseudomonas are stagnation, low levels or lack of biocides, the presence of nutrients, low water temperatures and reliance on UV treatment alone.
Lower respiratory infections can be caused by nontuberculosis mycobacteria (NTMs), e.g. ‘hot tub lung,’ causing shortness of breath, fatigue and enlarged lymph nodes. Risk factors in water systems are automatic taps, low chlorine levels, low hot water temperatures, plastic pipe work and biofilms.
Dr Lee emphasised that Legionella outbreaks occur because not enough prevention measures are being taken. Stagnation, nutrients, other microorganisms and lack of appropriate biocide concentrations will increase the risk. She emphasised the importance of carrying out a risk assessment (RA) of all systems that contain water where the whole or part of the system is between 20°C and 45°C , to identify the likelihood of a Legionella ‘hazard’ occurring and causing harm.
There are two important new guidance documents for the RA process, WHO guidelines on water safety in buildings and the British Standards Code of Practice for Legionella control BS8580. The latter covers initial risk assessment, review and audit for all artificial water systems but does not cover natural water systems, or control schemes. The scheme of control should be put together once the risks have been assessed.
Three major components are emphasised: desktop appraisal of documentation, site visit and reporting. Desktop appraisal should include records of previous risk assessments to allow focus on areas of most concern during the site visit. Good communication between the person carrying out the risk assessment and those commissioning it is also emphasised.
The chain of causation should be considered and emphasis is placed on agreement between the risk assessor and the commissioner of the RA on the scope of the RA. Previous management responses to problems must be reviewed and efficient reporting to provide effective prioritising of remedial actions. She concluded reviewing other practical codes and guidance, i.e. the HSE ACoP and Guidance L8 from 2000 and the 2006 HPA/HSE Management of spa pools.
Spotlight on Legionella
Control of Legionella was also highlighted by Dr Tom Makin, a leading international consultant, co-author of HSE ACoP (L8) and HTM 04-01 and expert witness in many legal cases.
“High numbers are needed to cause infection in healthy individuals but we only see the tip of iceberg and probably miss 95% of cases due to our poor ability to diagnose these infections.” Outbreaks of Legionnaires’ disease in Europe are reported to the European Centre for Disease Prevention and Control (ECDC), which carries a list on its website of all hotels that have not taken the recommended actions.
Potable water systems
Many cases of Legionnaire’s Disease originate in potable water systems because of under-used and stagnant parts of the system that encourage growth. He stressed: “you need to keep your hot water above 60°C and your cold water below 20°C as an effective control for Legionella.”
He also emphasised that thermostatic mixing valves are problematic because they produce water at a temperature suitable for bathing but which also supports Legionella growth. He observed that some ‘hands free’ taps and showers popular in hotels can be problematic as the more complex designs appear to support the presence of Legionella and other potentially harmful bacteria.
Dr Makin reported that energy conservation requirements in new buildings are making cold water systems more vulnerable to microbial contamination. Heat is now better retained in buildings and sinks into the lowest temperature it can find, normally the cold water system.
The main methods of controlling the risk of legionellosis are maintaining high and low temperatures; chlorine dioxide, which is around five times more effective at attacking biofilm than chlorine; copper and silver ions; and silver and hydrogen peroxide.
Regular flushing of outlets to prevent water stasis and the build-up of microorganisms is important, “in future, given need to maximize energy efficiency and save water means we will really have to consider if we can afford to maintain such high temperatures in hot water systems and continue to flush outlets.”
Concluding, Dr Makin emphasized that point-of -use-filtration (POU), using a 0.2 μm filter on taps and showers is “the only guaranteed way to prevent exposure to any microorganisms in a water system as none of the discussed control methods will completely eradicate microorganisms. As we now have to think more than ever about saving water and energy, it would be worth considering fitting POU filters to all showers, and possibly tap outlets in hotels to avoid using control measures that are at odds with sustainable development.” Dr Makin added, “this approach would not only reliably prevent infections caused by waterborne bacteria, protozoa and pathogenic fungi but could also be an effective deterrent to the increasing risk of litigation witnessed in the leisure industries.
Some sources of waterborne infection in the leisure industry
• Showers and taps
• Whirlpool spas and swimming pools
• Hot tubs
• Cooling towers/evaporative condensers
• Ice machines
• Bottled water dispensers
• Flushing toilets
• Ornamental fountains
• Play area water features
• Misting machines
• Irrigation systems
• Fire hoses and sprinklers
• Jet washers (notably for deck washing)
Legionella in a Spanish hotel
Dr Sebastian Crespí , Department Head of Clinical Laboratories Policlinica Miramar , Palma de Majorca, Spain , independent consultant and Director of Biolinea described four recurrent cases of Legionnaires’ disease after an initial cluster alert. Three risk assessments and several disinfections of the entire domestic water system were carried out and one of the victims died.
None of the samples were positive and despite strong positive epidemiological evidence, risk assessors concluded that the hotel was unlikely to be the source of the Legionella infections. A further case was reported in March 2006.
Dr Crespí’s team noted that water from the hotel’s two potable water tanks was filtered before circulating to the domestic water distribution system, and softened before reaching the hot water calorifiers and kitchen. An irrigation system was fed by water from the sewage plant, and there were two whirlpool baths and a fire fighting system. Water was chlorinated by dosing pumps.
Chlorine levels, pH and temperature were satisfactory in the first tank, but the second had much lower temperatures and chlorine levels. This was kept as a stand-by for water storage, leading to stagnation.
The calorifiers showed a return temperature of 57°C. However, temperatures on the higher floors were below 50°C. Inefficient recirculation was shown and the return valves adjusted accordingly.
The tanks, kitchen and irrigation system had good chlorine levels, but none was detected in other areas, despite the chlorine pumps operating correctly. The dosing pump of the corrosion inhibitor was found to be broken and was dosed via the line from the chlorine container which no longer served the pumps.
The fire fighting system, full of stagnant water, was found to discharge into one of the potable water tanks each time it was tested.
Positives were found both in the fire fighting system and in the softeners, neither of which had been sampled previously. “The lesson here,” Dr Crespi warned, “is that negative water results can always change. The results are dependant on sampling the right site, in the right context and on the lab that tests the samples.”
He noted that this case is a good example of what can happen when all the classical risk factors for Legionella growth converge alongside ‘emergent’ risk factors such as poor technical design, overconfidence in persistent negative results, poor staff training and a ‘risky’ risk assessment.
1. ‘Water safety in buildings’, WHO, March 2011 http://www.who.int/water_ sanitation_health/publications/2011/9789241548106/en/index.html
2. British Standards BS8580, Water Quality – risk assessments for Legionella control – Code Of Practice
3. Management of Spa Pools – Controlling the risks of infection. A Joint HSE and HPA Spa Pools Working Group. ISBN 0901144800.
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