Legionella in Building Water Systems
Risk Assessment and Proactive Monitoring
HBI’s Legionella Risk Assessment and Control Program
HBI has developed a state-of-the-art risk assessment and control program where assets are assessed and records electronically kept and updated on-line. This ensures consistent and cohesive policies for Legionella risk assessment and control across a portfolio of buildings.
HBI’s Identification and Assessment of Risk
At the time of the risk assessment HBI Field Technicians evaluate all the relevant factors affecting the condition of the water source, such as, system design, accessibility to airborne contamination, exposure to light, circulation rate, pH, temperature, droplet formation, water treatment program, etc. Assessment of the hazards then permits high-risk sources to be identified and ensures that responsible means of implementing precautions are undertaken.
As the likelihood of future contamination can be predicted this also allows maintenance regimes and water treatment protocols to be established on the basis of need rather than on guesswork.
Regular Monitoring – System of Control
The HBI sampling protocol is designed to ensure accuracy, avoid ambiguity, and protect client confidentiality and to aid in diagnosis of contaminated water systems.
Water from cooling towers, spray-type humidifiers and other air conditioning associated equipment present the greatest degree of risk and a routine sampling procedure from their water storage reservoirs and from other water systems can be set up. This allows management to have up-to-date reports on the status of their building water systems and gives confidence that maintenance standards are being met. Tenants, staff and building users can then be assured that all reasonable precautions are being taken to avoid the spread of Legionnaires’ disease.
Furthermore, immediately prior to routine cleaning and maintenance, if appropriate, cooling towers and humidifiers can be tested for the presence of legionella. If it is found to be present then the necessary water treatment can be done, quickly verified for its effectiveness and engineering staff assured that they will not be exposed to microbial hazards as they carry out the work. Hot and cold water services and other water systems can similarly be appraised for risk and a suitable system of maintenance, cleaning and testing implemented.
Background
In July 1976 in Philadelphia an outbreak of pneumonia affected 221 people, killing 34. Many were members of the American Legion attending a convention in the Bellevue-Stratford Hotel. The causative organism, Legionella pneumophila, is widely distributed in nature and although positively identified and named only several months after the outbreak of the illness that gave the disease its name, legionnaires' disease, it has probably been causing infections in humans for hundreds of years.
More than 30 species of legionella and at least 14 serogroups of Legionella pneumophila have now been identified, however the Pontiac sub-type (MAb2) of Legionella pneumophila Serogroup One is responsible for more than 90% of known infections. OSHA states that “Approximately 1,000 cases are reported annually to the CDC, but it is estimated that over 25,000 cases of the illness occur each year and cause more than 4,000 deaths.”
Habitat
Legionella species occur naturally in soil, rivers and lakes and have the ability to successfully colonise man-made water handling and storage systems, which often provide ideal conditions of nutrition and temperature for their proliferation. Legionella infection is not transmissible from person to person; it is caused by the inhalation of water aerosols containing the bacteria by susceptible individuals. The numbers of organisms required to induce infection is not known but will vary according to age, general health and other predisposing factors.
The potential for legionella to become a hazard to the health of large numbers of people is greatly enhanced by conventional water and air conditioning engineering methods as used in re-circulating cooling towers, evaporative condensers, showers, water storage and distribution systems and other aquatic systems such as whirlpool spa baths.
Cooling Towers and Water Storage Systems
The single isolation of these bacteria from a water system does not mean that the disease will necessarily manifest itself but if the contaminated water becomes an aerosol the risk of human infection is greatly increased. Thus if man-made water systems produce jets, sprays or mists, as with cooling towers, showers and some types of humidifiers, it is important to minimize the chances of legionella colonizing the water reservoirs, storage tanks and other aquatic systems serving them. Certainly cooling towers are of particular importance for their operating temperatures are at an optimum level; they are designed to aerosolize the water and they are easily and frequently contaminated by wind-blown dusts and soil particles which can carry with them disease producing micro-organisms including legionella.
The presence of these bacteria in water systems is therefore of prime importance to engineers, building managers and hygienists. The organisms can be controlled in such systems by the application of biocides and their detection and identification plays a vital role both in initial assessment of the water system and subsequent treatment effectiveness and ongoing water quality monitoring.
Standards of Care
There are two main Standards of Care in the United States and an internationally recognized one in the United Kingdom. They are broadly consistent in their guidance for risk analysis followed by a systems of control, or maintenance procedure for “at risk” systems. ASHRAE - 12-2000 Environmental and operational guidance for minimizing Legionella contamination in building water systems.
ASHRAE is currently in the process of converting the "guideline" into an official Standard, designated "SPC 188." The standard will result in an affirmative duty upon building owners to establish Legionella auditing and prevention programs.
The new standard will include language on Legionella hazard analysis, whereas the current 12-2000 guideline does not.
The goal is to eliminate the Legionella hazard in building water systems or reduce it to an extent that prevents harm to people. The Hazard Analysis Critical Control Point (HACCP) system has been proven successful for preventing environmental-source disease, is widely endorsed worldwide and is intended to prevent Legionellosis associated with building water systems.
Hazard (or risk) analysis and control implementation shall include seven elements:
Hazard Analysis
1. Identification of critical control points;
2. Establishment of critical limits at critical control points;
3. Establishment of a monitoring plan for critical limits at critical control points;
4. Establishment of corrective actions for each critical limit;
5. Establishment of procedures to document all activities and results;
6. Establishment of procedures to confirm that a) the hazard had been eliminated or controlled under operating conditions (validation), b) the plan is being implemented properly (verifications) and c) the plan is periodically reassessed.
OSHA Technical Manual
OSHA publishes guidelines and recommendations for the control of Legionella with a two-level approach to diagnosing the building water system:
www.osha.gov/dts/osta/otm/otm_iii/otm_iii_7.html.
As a cognizant authority in the US, it represents a defensible source of reference for building owners to follow. After a reported case of Legionnaires’ disease this manual should be consulted for procedures for treatment, testing and monitoring actions. To quote OSHA, “A level-one investigation may be initiated when there is a probable basis for suspecting that workplace water sources are contaminated with legionella, or when there is information that one case of Legionnaires' disease may exist. A level-two investigation should be conducted when more then one possible case of Legionnaires' disease has been reported at a facility.”
The Level One investigation consists of an overview of the building water systems via a walkthrough, an identification of components that may present a risk and any recent changes in the system.
If more than two cases of Legionnaires’ disease have been traced to a particular building, this is considered an “outbreak” and the Level One procedures should be supplemented by medical surveillance of building occupants out on sick leave, employee awareness training, a historical assessment of sick-leave records, and water sampling. Medically, Legionnaires’ disease is a reportable condition in most states, but this does not necessarily mean that the building owner is required to report conditions or results of the control program in the building. Local regulations on this matter should be consulted.
United Kingdom ACoP L8
The British Health & Safety at Work Act 1974 (HSWA) and Control of Substances Hazardous to Health Regulations 1988 (COSHH) include for the risks from hazardous micro-organisms, including legionella. Under the Regulations risk assessments and the adoption of appropriate precautions are required to be made. Furthermore, the Approved Code of Practice and Guidance L8 (Legionnaires' disease. The control of legionella bacteria in water systems), (the ACoP), sets out statutory requirements for dealing with such risk. The ACoP applies to the risk from legionella bacteria in any circumstances where the HSWA applies. In order to comply with their legal duties, as detailed in the ACoP, employers and those with responsibility for the control of premises should:
- Identify and assess sources of risk, (the ACoP dictates that persons responsible for undertaking the risk assessment need to have access to competent help and advice)
- Prepare a scheme for preventing or controlling the risk;
- Implement, manage and monitor precautions;
- Keep records of the precautions; and
- Appoint a person to be managerially responsible.
Because of its widespread presence in nature and its ability to thrive in man made water systems it is unlikely that legionella can be completely or permanently eradicated from these potentially hazardous systems. However, by suitable design, maintenance, treatment and testing of building water systems it is possible to control the conditions which allow this and other bacteria, fungi and protozoans to multiply, thus keeping the incidence of disease outbreaks associated with such systems at a minimum. Any Proactive Monitoring System applied to buildings and their water systems should therefore include regular monitoring for the presence of legionella at appropriate outlets.
The increased public awareness of environmental health issues and the acceptance of the legislation now approved have ensured that risk assessment and appropriate preventative maintenance steps, should now be considered as the norm for every building.
