Legionnaire's Disease and Plumbing Design
By Susan Ecker,
Technical editor, Plumbing Engineer
On July 21-24, 1976, the Bellevue-Stratford Hotel in Philadelphia hosted the 58th Pennsylvania State Convention of the American Legion. More than 4,000 World War II Legionnaires took part in the event. Approximately 600 of them stayed at the Bellevue-Stratford. The day after the convention opened, a number of the participants became ill. The symptoms were flu-like and consisted of fever, coughing, breathing difficulties, chest pains, lung congestion and pneumonia. In the days that followed the convention, the still unidentified disease killed 34 participants and infected 221, all of whom had spent time at the hotel. The ages of those who died ranged from 39 to 82 years.
On January 18, 1977, scientists discovered the cause of the Philadelphia deaths, a bacterium that had not yet been named. On November 18,1978, the bacterium was given a scientific name: Legionella (to honor the victims of the Legionnaires' convention) pneumophila (pneumonia symptoms that occurred in Philadelphia). The disease became commonly known as Legionnaires' disease.
Researchers still had to determine how the disease was transmitted. Legionella pneumophila resembled bacteria that one researcher had found in the thermal regions of Yellowstone National Park, where it tended to live as biofilm (scum) associated with certain species of algae. Subsequently, scientists began investigating aquatic habitats and found the bacteria residing in thermal waters discharged from a nuclear reactor at Savannah River Laboratory, in natural hot springs all over the United States and in air conditioning cooling towers.
Of the 221 people who became sick in Philadelphia, 72 were people not involved in the American Legion convention. These people had either been inside the Bellevue-Stratford Hotel or had walked past it. The Legionnaires' disease bacillus was actually spread by the air conditioning system in aerosolized water droplets. People who inhaled the aerosols also inhaled the microorganisms, which were brought into the respiratory tract. There they multiplied without interference from the immune system, causing flu-like symptoms and, when left untreated, pneumonia that resulted in death. Other outbreaks and epidemics occurring throughout the world since then have revealed that the occurrence of Legionella in manmade environments was not restricted to cooling towers alone; that wherever on earth there was a machine that could produce mist, there was Legionella and Legionnaires' disease. It was later found that the bacteria could also colonize and amplify (the exponential growth of the organism) in domestic water systems, such as the hot water system.
What is Legionnaire's Disease?
Legionnaires' disease and Pontiac Fever are two forms of the disease caused by several species of the Legionella bacteria. Collectively, these two diseases are called legionellosis. Both are transmitted through airway exposure; there has been no reported human-to-human transmission of the bacteria. The primary source of human exposure is airborne water droplets or mists from contaminated water sources.
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| Legionella is water borne and can be aerosolized. They may survive as long as 139 days at room temperature in distilled water and for more than a year in tap water. |
Legionnaires' disease is a form of pneumonia and includes symptoms of pneumonia. It affects mostly smokers, transplant patients, the elderly and immuno-compromised people. Usually, less than 5% of exposed people develop the disease. On occasion, if patients are not appropriately treated, death is likely, and the fatality rate may reach 15%. If it is diagnosed early, Legionnaires' disease is treatable with antibiotics.
Fever and flu-like illness are the primary symptoms of Pontiac Fever, a milder form of the disease caused by Legionella bacteria. This disease is not considered lethal. However, more than 95% of the exposed population may develop symptoms after a short incubation period. A full recovery follows after a couple of days.
Legionella bacteria can survive in a temperature range of 68 - 122 F and grow in a temperature range of 77 - 108 F. There are indications that they can survive in temperatures lesser than 68 F. Temperatures approaching 131 F start to kill the organism. This information makes it clear that the bacteria can grow in cooling tower water or in domestic hot water systems, specifically those systems set at a tepid water temperature range. High temperatures, greater than 131 F, can be used to control the bacteria.
Legionella is water borne and can be aerosolized. They may survive as long as 139 days at room temperature in distilled water and for more than a year in tap water. They thrive, not just survive, in tap water, where they establish a symbiotic relationship with a variety of protozoa and amoebae, and grow and multiply inside the protozoa and amoebae. This association makes treatment to get rid of the bacteria much more difficult.
The organisms can survive in aerosols and have been found as far as two miles away from the aerosol source. They have been found to spread through Heating, Ventilation and Air Conditioning (HVAC) systems when the bacteria growing in the cooling tower are aerosolized and get into the air handling system air intake. In addition to cooling tower water, Legionella bacteria have been isolated from potable water supplies, lakes, soils, etc.2
Plumbing
Legionella bacteria are very common in surface water; this is how the organism enters the domestic water system. These bacteria are known to survive in and colonize domestic water systems, especially hot water systems, where they are difficult to control because they may hide and survive in the biofilm on the surface of the pipes. The concentrations of Legionella bacteria in building water supplies are typically very low and may not be detectable in routine sampling and testing of the water supply.
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| A variety of aerosol producing devices have been associated with outbreaks of Legionnaires' disease including showers. |
It only takes a small amount to colonize the water system. Older water systems have thicker biofilm buildup and are more likely to have Legionella colonization. Because Legionella amplification requires warm water temperatures, hot water systems, dead legs, corners of the pipes and hot water heaters are susceptible. Temperature stratification in a heater can allow Legionella bacteria to survive and even amplify. Biofilm on the interior surfaces of the water system can protect the bacteria from exceedingly high temperatures.
The American Society of Heating Refrigeration and Air Conditioning (ASHRAE) has created a guideline ASHRAE Guideline12 - Minimizing the Risk of Legionellosis Associated with Building Water Systems. The following are excerpts from the ASHRAE guideline.
"Natural rubbers, wood, and some plastics have been shown to support the amplification of Legionella, while other materials, such as copper, inhibit their growth. A variety of aerosol producing devices have been associated with outbreaks of Legionnaires' disease including cooling towers, evaporative condensers, showers, whirlpool spas, humidifiers, decorative fountains, and a grocery store produce mister. Aspiration of colonized drinking water into the lungs has been suggested as the mode of transmission in some cases of hospital acquired Legionnaires' disease."
"Growth of Legionella may occur in portions of the plumbing system with infrequent use, in stagnant water, and in portions of the system with tepid temperatures. Growth may also occur in dead end lines, attached hoses, shower nozzles, tap faucets, hot water tanks and reservoirs. Rubber washers and fittings, including water hammer arrestors and rubber hoses with spray attachments have been shown to provide sites for the growth of Legionella. Organic compounds leached from plumbing materials may contribute to the growth of Legionella."
"Safety showers, eyewash stations and fire protection systems are plumbed to the potable water system and have stagnant water sitting in the pipes that may reach temperatures higher than ambient. When these systems are utilized, aerosolization is expected to occur. There have been no reported cases of legionellosis resulting from exposures to aerosols produced by these systems."
Prevention
According to ASHRAE Guideline 12 the following recommendations should be followed in order to prevent legionellosis. For a complete explanation, see the ASHRAE guideline.
- Hot water should be stored at temperatures of 120 F, or above.
- Elevated holding tanks for hot and cold water should be inspected and cleaned annually.
- Copper silver ionization should be used for high-risk applications such as hospitals.
- In high-risk applications, showerheads and faucet aerators should be removed monthly to clean out sediment and scale and to clean them in chlorine bleach.
- Emergency shower and eyewash stations should be flushed at least monthly.
- During the release of fire water during a fire emergency it is assumed that fire department personnel will be wearing protective respiratory equipment and that non-fire fighting personnel will exit the burning area.
- Appropriate precautions should be taken when testing the fire protection system.
- High temperature flushing or chlorination is recommended.
Conclusion
Many of the recommended methods of preventing infection with Legionnaires' disease require routine maintenance. These practices must be performed regularly and documented. Plumbing engineers should design systems that can be easily maintained and that minimize "deadleg" plumbing. Both plumbing engineers and facility engineers play a vital role in the prevention of Legionnaires' disease.
References
Susan R. Ecker is a senior plumbing engineer with Rumsey Engineers Inc. in Oakland, Calif. and technical editor of Plumbing Engineer. She has extensive experience in designing plumbing systems for industrial and commercial market sectors. Susan can be reached at secker@rumseyengineers.com.