Legionella is a ubiquitous organism, a rod-shaped bacterium found in natural water resources, viz: rivers, lakes, streams, soil samples, including drinking water sources like wells, etc.
Following the 1976 American Legion Convention in Bellevue Stratford Hotel in Philadelphia, 34 attendees died and 221 people became ill from pneumonia. The infection was eventually researched and attributed to organisms residing in the water stored in the cooling towers being spread by air-conditioning system itself, in aerosolised water droplets.
Being associated with the American Legion, the Bacterium was named Legionella Pnuemophila and the associated disease called Legionnaire disease.
Legionella occurs in very low concentrations and typically thrive and proliferate in a warm and damp environment in manmade water systems, at temperatures ranging from 20C to 45C e.g. Cooling Tower drifts, lagoons, spas and domestic water systems and even swimming pools, if not treated adequately.
Legionnaire Disease is a respiratory infection that usually strikes individuals with weak immune systems. Heavy smokers, especially, male above 50 years of age are more susceptible. Infection results from inhaling airborne water droplets or mist containing viable count of Legionella which are small enough to pass deep into the lungs and get deposited in the alveoli. The incubation period can vary from 2 – 10 days. Symptoms vary from high fever, chills, headache, muscle pain and at times dry cough may develop leading to breathing difficulty and a feeling of disorientation.
Legionnaires Disease Causation in Healthcare Facilities
A typical healthcare unit consists of various equipment and water systems which pose a risk for growth of Legionella bacteria and triggering the onset of Legionnaires Disease. The equipment includes dental water lines, respiratory therapy gadgets and water therapy tubs systems to basic facilities like faucet aerators, shower heads and decorative fountains, all being aerosol generating systems.
The Crux of ASHRAE standard 188-2015
Legionellosis is ‘Recognised as Hazard’
Healthcare facilities either housing patients for more than 24 hours or treating patients for burns, chemotherapy ,organ or bone marrow transplantation, liable to comply.
Code Recommendations for Healthcare Facilities
Develop a Legionella management plan to include:
o Environment assessment which includes description and documentation of the building water system and conducting a detailed risk assessment and hazard analysis.
o Preventive maintenance which includes development and implementation of Water management plans and adoption of engineering controls.
o Sampling and Validation, identifying water sampling points based on risk systems, conducting Legionella Specific Water Analysis from a NABL certified lab and validation of engineering controls based on lab reports.
Water Safety Organisational Group for Hospitals
There is code requirement for a team of experts referred to as the Water Safety Group or WSG. In healthcare environments, the WSG describes a team of specialists that collectively has the responsibility for creating, implementing, and maintaining a Water Safety Plan (WSP). This plan is designed to ensure that the water used in hospitals and similar healthcare settings is safe to use by patients, staff and visitors, and poses minimal risk of infection from waterborne pathogens i.e. through the presence of legionella bacteria, pseudomonas and other unwanted contaminants.
Primary Role of the Water Safety Group
The Water Safety Group through its team of experts should take responsibility for the identification and assessment of water-related hazards, the development of suitable monitoring and control measures to minimise the risks, and the creation of suitable incident protocols.
Who should be part of the WSG?
Ideally, the Water Safety Group should have several team members, each of whom brings a particular skill set to the table. For example, one might have extensive engineering knowledge relating to water systems. Another might have experience of working with water in a healthcare setting, thereby, understanding the potential risks that a system poses. This approach ensures that the group has the required extensive knowledge and experience that would be impossible to glean from just one person.
Typically, the WSG would include people from some or all of the following specialist areas:
- Property and estates management including operations and projects
- Infection control
- Medical microbiology
- Nursing
- Augmented care
- Housekeeping/support services
- Authorising Engineer (Water)
- Medical technical officers
- Specialist users of water (such as renal units and departments offering aquatic therapy)
- Sterile services departments (SSDs)
Accountability and Group Structure
Ultimately, the duty holder is responsible for the maintenance and safety of the water systems in use throughout a hospital or healthcare facility. The duty holder may be a business owner, a board of directors, an NHS Trust, its Chief Executive, a director or senior manager, but should be clearly identified at the outset. Whoever this is will depend on the organisation and the circumstances. However, the entire WSG should be responsible to the duty holder and be organised with clear accountability in mind. Each person should be aware of their role within the group, and of the responsibilities they have. A typical structure for a Water Safety Group can be seen on the nest page.
Water Disinfection Strategies to inhibit growth of Legionella Bacteria
Heat : Constant Temp control and Thermal Shock
Constant maintenance of the temperature between 55-60°C
At 60C, it takes approximately two minutes to inactivate 90 per cent of a population of Legionella pneumophila. The effectiveness of maintaining the circulating temperature at 60C has been demonstrated both in hospitals and in hotels. Hot water installations maintained at temperatures above 50C are less frequently colonised by Legionella. Circulating water at 60C such that the temperature at each outlet reaches at least 50C and preferably 55C within one minute of opening the outlet, is the method most commonly used to control legionella in hot water distribution systems. Although raising the temperature to a constant 60C has consistently been shown to control outbreaks it does not necessarily eliminate Legionella from the system but controls them at a level that prevents further cases. Provided, there is sufficient heating capacity it is relatively easy to implement and is easy to monitor continuously. It has the possible disadvantage of increasing energy consumption and there is an increased risk of scalding. Where thermostatic mixer valves are installed to reduce scalding risk, they must be subjected to a program of planned monitoring and maintenance
Thermal shock
Thermal shock treatment at 70-80C for relatively short periods has been used both for emergency disinfection, and also for periodic disinfection of systems, as part of long-term control programs.
Thermal disinfection is carried out by raising the temperature of the whole of the contents of the hot water storage heater to 70-80C then circulating this water throughout the system for up to three days. To be effective, the temperature at the hot water storage heater should be high enough to ensure that the temperatures at the taps and appliances do not fall below 65C. Each tap and appliance should be run sequentially for at least five minutes at the full temperature, and this should be measured. For effective thermal disinfection, the water system needs to be well insulated. Some recommend emptying the hot water tanks in advance, cleaning them and decontaminating them with chlorine (50 mg/l for one hour or an equivalent) but this may cause corrosion.
It is essential to check that during the procedure, the temperature of the water in distal points reaches or exceeds 65C.
At the end of the procedure, samples of water and sediment should be
collected at distal points of the installation and examined for Legionella. If the result
is unsatisfactory, the procedure must
be repeated until documented decontamination is achieved. Following decontamination, microbiological checks must be repeated periodically.
Thermal treatment has the advantages that no particular equipment is required so that the procedure can be carried out immediately, provided there is sufficient heat capacity in the system. However, the procedure requires considerable energy and manpower and is not normally practical for large buildings but may be suitable for small systems. It will not disinfect downstream of thermostatic mixer valves and so is of limited value where such valves are installed. There is a severe risk of scalding at these temperatures. Although the numbers of Legionella may be reduced, recolonisation of the water system can occur from as little as a few weeks after treatment, particularly, if it has not been accompanied by other remedial measures.
Chlorination
Chlorine has also been used for the treatment of hot water systems. As the bactericidal action of the chlorine is pH sensitive and decreases rapidly at values above 7 the pH of the water will have to be monitored and may need adjustment.
Shock hyperchlorination
This must be carried out in water at a temperature below 30C with a single addition of chlorine to the water to obtain concentrations of free residual chlorine of 20-50 mg/l throughout the installation, including distal points. After a contact period of at least two hours with 20 mg/l of chlorine or at least one hour with 50 mg/l of chlorine, the water is drained. Fresh water is then let into the installation until the level of chlorine returns to the concentration of 0.5-1 mg/l.
Continuous chlorination
This is achieved by the continuous addition of chlorine, usually in the form of calcium hypochlorite or sodium hypochlorite. Residual levels of chlorine can vary depending on the quality of the water, the flow, and the amount of the biofilm in the system. However, the residual disinfectant must be between one and two mg/l. Where there are stagnant areas or circulation problems in the water distribution system, the chlorine will not inactivate Legionella in these areas. Although continuous chlorination has been used as a means of control in hot water systems, it is difficult to maintain the required levels of chlorine as it volatilises off from hot water. In addition, chlorine is corrosive and this effect is increased with raised temperatures.
Chlorine dioxide
Chlorine dioxide has been successfully used to control Legionella in some hot water systems and can be used in the same manner as chlorine. It has the advantage that it is not as volatile at high temperatures as chlorine and is said to be more active on biofilms.
Monochloramine
There is some evidence that hospitals receiving water that has been treated with monochloramine rather than chlorine are less likely to have outbreaks of legionnaires’ disease and are less colonised with Legionella. It is possible that treating hot water systems with monochloramine may prove more effective than chlorine but appropriate dosing systems are not yet available for buildings. Monochloramine is slower acting than chlorine but persists longer and is therefore, said to be more effective against biofilms.
Cu/Ag Ionisation
“Ionisation” is the term given to the electrolytic generation of copper and silver ions for use as a water treatment. Metals such as copper and silver are well known bactericidal agents. They act on the cell wall of the micro-organism that alters the cells permeability which, together with protein denaturisation, lead to cell lysis and death.
Copper and silver ions are generated electrolytically and their concentration in the water depends on the power applied to the electrodes. Copper and silver ion concentrations maintained at 400 µg/l and 40 µg/l respectively can, if properly managed be effective against Legionella in the planktonic and biofilm phase in hot water systems. If, however, the water is softened then silver ion concentrations between 30 to 20 µg/l can also be effective, provided a minimum concentration of 20 µg/l is maintained. This level of silver still requires copper ions to complete the synergy.
The application of ionisation will need to be properly assessed, designed and maintained as part of an overall water treatment program. It should be noted that in hard water systems, silver ion concentrations can be difficult to maintain due to build up of scale on the electrodes, unless anti-scaling electrode cells are employed. High concentrations of dissolved solids may precipitate the silver ions out of solution. For both hard and soft water, the ionisation process is pH sensitive and it is difficult to maintain silver ion concentrations above pH 7.6. The build-up of scale and concentration of dissolved solids therefore needs to be carefully controlled so that suitable ion levels are consistently maintained throughout the system. This may require additional water treatments.
The method is easy to apply and is not affected by the temperature of the water. However, because the system is subject to fluctuations in concentration unless automatic controls are employed, it is necessary to check the concentration of the two metals regularly, as well as the pH of the water at 6-8. This technique is not suitable for systems that employ zinc cathodic protection for water systems because the metal deactivates silver ions. Furthermore, if the treatment is used continuously it is necessary to check that the maximum permissible concentration (CMA) laid down by current legislation for drinking water is not exceeded.
Hydrogen peroxide and silver
Treatment is carried out using a stable concentrated solution of hydrogen peroxide (oxygenated water) and silver, exploiting the bactericidal action of each of the two components and the synergy between them. The technique is relatively recent and requires further experimental confirmation.
Ultraviolet (UV) radiation
Irradiation with ultraviolet light is an alternative method for the disinfection of drinking water. Ultraviolet light (254 nn) inactivates bacteria by producing thymine dimers in their DNA that inhibit replication. The application of ultra-violet light is a method of disinfection that has proven effective close to the point of use. The thermal shock and chlorination methods can be used prior to application of ultraviolet light to control Legionella present in the system. UV equipment is relatively easy to install and has no adverse effects on the taste or potability of the water and does not damage piping. The technique is not suitable as the only method for an entire building or water system because there is no residual effect, and Legionella remains in the biofilms, dead ends and stagnant areas of the system.
Conclusion
It can be inferred from the above, that controlling Legionella Bacteria is not an expensive affair. It involves proper design and thereafter pursuit of an appropriate operation and maintenance schedule which needs to be followed diligently. With these simple but critical measures, Legionella Bacteria can be controlled effectively and maintained below limits that may cause detrimental health effects.
In conclusion, Legionella Compliance is definitely the way forward for the healthcare facilities to protect their brand image and ensure continuity of business.
