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Legionella Bacteria is Widespread Legionella bacteria are widespread in the environment. Both man made and natural water sources provide habitat. In nature these bacteria exist at low levels in slime and biofilms. The bacteria are not completely eliminated by the chlorination used to purify domestic water supplies. In the industrial environment and in health care facilities, bacteria present in purified water sources can increase dramatically if given the right conditions. Bacteria Thrive Under Certain Conditions These conditions include warm stagnant water with temperatures between 68° and 122°F. Ideal growth occurs at temperatures of 77°-108°F (25°-42°C) and a pH between 5.0 and 8.5. Sediment from rust (iron), and scale in water systems can also promote growth. Algae and other microorganisms can provide habitat and nutrients for the protozoa and bacteria that promote legionella growth. Identification of possible locations where these conditions exist is essential to controlling sources of this disease. These locations include
When an industrial process or air conditioning system generates a mist from contaminated water the microorganism becomes an airborne hazard. Drinking contaminated water may also lead to disease. General Guidelines for Control of Bacteria Specific guidelines to control growth and spread of legionella are contained in OSHA Technical Manual Section III: Chapter 7 and in the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Guideline 12-2000, Minimizing the Risk of Legionellosis Associated with Building Water Systems, 2000. In general the guidelines focus on eliminating the conditions that allow bacteria to thrive. These guidelines include:
Regularly maintain and clean cooling towers and evaporative condensers to prevent growth of legionella. This should include twice yearly cleaning and periodic use of chlorine or other effective biocides. If the system will be inoperative for three or more days ASHRAE recommends completely draining a system (cooling tower, system piping heat exchangers, etc.) Upon start up the system should be refilled and treated with appropriate biocide or treated with sodium hypochlorite to a level of 4-5mg/L free chlorine. This level should be maintained for six hours. Only after treatment should fans be turned on. Detailed operation and maintenance records should be kept. Maintain domestic water heaters at 140°F (60°C). The temperature of the water should be 122°F or higher at the faucet. If hot water systems need to be decontaminated hot water temperatures should be raised to 160-170°F (71-77°C) and flushed for at least 5 minutes from all taps. Multiple 30-minute flushes may be required to reduce legionella bacteria levels. Where thermal shock is not possible chlorination can be used. Chlorine must be maintained throughout the system for at least two hours at a level of 2mg/L (2ppm). All taps should be run until a distinct odor of chlorine is present. Bacteria tend to accumulate in the bottom of hot water heaters. Installing destratification pumps in large heaters will mix water and kill bacteria. For cold water systems pipes should be segregated or insulated to avoid temperatures above 20°C (68°F). Avoid conditions that allow water to stagnate. Large water storage tanks exposed to sunlight can produce warm conditions favorable to high levels of legionella. Frequent flushing of unused water lines will help alleviate stagnation. Unused plumbing sections (dead legs) should be drained or eliminated. Properly maintained HVAC systems will not breed bacteria, but may be a source of spreading bacteria. If HVAC air intakes are located near or down wind from cooling towers or evaporators that are generating contaminated mist the bacteria could be distribute throught he HVAC ductwork. HVAC systems with humidifiers can become breeding ground. Sumps and pans should be drained and cleaned regularly. Infrequently used faucets and showers may harbor bacteria. Showerheads and aerators should be cleaned. Rubber washers and fittings provide habitat for bacteria and should be replaced. Rubber hoses with spray attachments should be cleaned with chlorine bleach solution. Safety showers and eyewash station should be flushed monthly. Increased risk of contamination occurs any time the water systems are opened for repair or construction. Anytime color changes occur in water systems after repair, the effected portion of the water system should be decontaminated. When to Sample for Bacteria Sampling for total bacteria is not enough. Specific tests for legionella is required for a good maintenance program. If there is a suspicion that water sources are contaminated or if a single case of Legionnaires’ disease exists, a thorough study of the water system is warranted. After the water systems have been systematically evaluated and control actions have been taken water should be sampled. Water should be collected under the guidance of an accredited lab. The laboratory will then attempt to grow the bacteria under controlled conditions. Contamination is expressed in number of colony forming units per milliliter of water (CFU/ml). The limit of detection for this analysis is 200-1000 CFU/liter. The following table should be used to interpret lab results and develop action plans.
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In
Great Britain companies are required to implement stringent controls
for water systems that can be a source of Legionnaires’ disease. Environmental
health officers aggressively enforce the law and can bring charges against
companies and individuals responsible for these control programs. Faced
with the possibility of significant fines and jail time, most organizations
are complying with the new laws. Legionnaires’ is a preventable disease.
Recent UAW fatalities demonstrate the terrible cost of not taking steps
to control this disease.
