Infection Control Today - 02/2002: Combating Legionella Bacteria

Combating Legionella Bacteria
Don't Let These "Swimmers" Sink Your Facility's Infection Control Program

By Kelly M. Pyrek

Editor's Note: This new department will appear quarterly in Infection Control Today, and is dedicated to informing facilities' staff members in environmental services and housekeeping departments.

here's nothing the Legionella pneumophila bacterium like better than doing the backstroke in a hospital's water-delivery system. The organism can reproduce rapidly in warm, stagnant water similar to what can be found in plumbing systems, whirlpool spas, hot water tanks, cooling towers, and evaporative condensers of air-conditioning systems. The bacteria can divide again and again with lightning speed, creating millions of cells after just a few hours or days within the optimal temperature of 98.6º F.

Outbreaks of legionellosis, the disease caused by the Legionella pneumophila bacteria, have been documented after people breathed the mist emanating from a contaminated water source; the disease cannot be transmitted from person-to-person contact.

Legionellosis takes two distinct forms; Legionnaires' disease is the more severe form of infection that includes pneumonia. Legionnaires' disease is named after a 1976 outbreak of pneumonia at an American Legion convention. Because of the size and severity of the outbreak, federal, state, and local health authorities launched the biggest cooperative investigation in history to determine the cause of the outbreak. All of the affected conventioneers eventually developed pneumonia, and ultimately, 34 of the 221 people who became ill, died.

Pontiac fever--named after the first documented outbreak among public health department employees in Pontiac, MI in 1968-- is a much milder illness. The 144 individuals who fell ill eventually recovered, and the bacteria were isolated from condensate water collected from the drip pan of an evaporative condenser located in the building's basement.

The Centers for Disease Control and Prevention (CDC) estimates as many as 15,000 individuals contract legionellosis in the US annually. Serologic surveys have indicated that numerous people in the general population have antibodies to legionellae, suggesting that large numbers of individuals may have been exposed and potentially infected with legionellae. Most outbreaks have been linked to aerosols contaminated with these organisms from evaporative condensers, potable water services and components such as whirlpool baths, as well as respiratory therapy equipment and even decorative fountains.

While some patients present mild symptoms, about 5-30% of them die from the legionellosis infection. An infection generally presents within 2-5 days of exposure to the bacterium. Symptoms include fever, chills, and a cough that may be dry or produce sputum, as well as muscle aches, headache, fatigue, loss of appetite, and occasional diarrhea. Chest X-rays often reveal the presence of pneumonia, while laboratory tests may point to kidney malfunctioning. Individuals with Pontiac fever exhibit symptoms within several hours to up to 10 days after exposure, and demonstrate fever and muscle aches. Patients tend to recover in 2 to 5 days without treatment. Legionellosis targets middle-aged and older individuals who may have chronic lung disease or whose immune system is suppressed by diseases such as cancer, diabetes, AIDS, or kidney failure that requires dialysis. Current treatment includes the antibiotic erythromycin, and in severe cases, rifampin.

Water is the reservoir for legionellae in the environment, and any natural or man-made system that provides suitable conditions for the growth and multiplication of Legionella is considered a potential amplifier, according to the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). Just a few organisms can be transmitted from the reservoir to a niche where they can grow to high levels. Examples of these amplifiers are humidifiers, potable water heaters and holding tanks, as well as showerheads, faucet aerators, and pipes that could contain stagnant warm water. Essentially, any water or water-conveyance system with favorable conditions for the growth of legionellae can become an amplifier.

According to an ASHRAE position paper, "Legionellae are carried in the treated drinking water to buildings where they enter and colonize the plumbing fixtures, especially of the domestic hot water system. Cooling towers and other wet-type-heat rejection systems also can become colonized if potable water containing legionellae (at very low numbers) is used as the source for their make-up water. This is probably the most frequent way equipment becomes contaminated even though some equipment--such as cooling towers--are excellent air scrubbers. Aerosolized legionellae contained in droplets may possibly be removed from the air and find a niche in open recirculating systems."

ASHRAE emphasizes that without a routine maintenance program, periodic monitoring for legionellae is not effective. The organization states, "More emphasis should be placed on clean equipment in excellent repair than on periodic testing with concurrent system neglect."

ASHRAE believes that if legionellae are prevented from amplifying in or on a device, the probability of having legionellae in sufficient concentrations to be infectious to a susceptible host is significantly reduced. The organization suggestions the following strategies for minimizing colonization and/or amplification of the bacteria:

  • Avoid piping that is capped and has no flow. If such piping exists after renovation it should be removed from both domestic and cooling water systems.
  • Control domestic water temperature to avoid temperature ranges where legionellae grow and to keep domestic cold water below 77º F and hot water above 131º F.
  • Apply biocides in accordance with label dosages to control the growth of bacteria, algae, and protozoa that could contribute to the nutritional needs of legionellae.
  • Limit the places legionellae can hide. Removing or preventing sediment accumulation in cooling basins, fountains, and hot water tanks can help minimize microbial niches.

Environmental services personnel can help cut down on aerosolization by doing the following:

  • Design cooling tower and building air intake placement so air discharged from the cooling tower or evaporative condenser is not directly brought into the facility's air intake.
  • Maintain effective drift eliminators on cooling towers and evaporative condensers.
  • Ensure that air filters for outside air are dry, since water droplets that condense on filters provide an environment where microbes can grow and could be dispersed to the conditioned space.

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