Infection Control Today - 02/2002: Combating Legionella Bacteria

February 1, 2002

Combating

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

By Kelly M. Pyrek

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

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

Outbreaks of legionellosis, the disease caused by the Legionellapneumophila bacteria, have been documented after people breathed the mistemanating from a contaminated water source; the disease cannot be transmittedfrom person-to-person contact.

Legionellosis takes two distinct forms; Legionnaires' disease is the moresevere form of infection that includes pneumonia. Legionnaires' disease is namedafter a 1976 outbreak of pneumonia at an American Legion convention. Because ofthe size and severity of the outbreak, federal, state, and local healthauthorities launched the biggest cooperative investigation in history todetermine the cause of the outbreak. All of the affected conventioneerseventually developed pneumonia, and ultimately, 34 of the 221 people who becameill, died.

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

The Centers for Disease Control and Prevention (CDC) estimates as many as15,000 individuals contract legionellosis in the US annually. Serologic surveyshave indicated that numerous people in the general population have antibodies tolegionellae, suggesting that large numbers of individuals may have been exposedand potentially infected with legionellae. Most outbreaks have been linked toaerosols contaminated with these organisms from evaporative condensers, potablewater services and components such as whirlpool baths, as well as respiratorytherapy equipment and even decorative fountains.

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

Water is the reservoir for legionellae in the environment, and any natural orman-made system that provides suitable conditions for the growth andmultiplication of Legionella is considered a potential amplifier,according to the American Society of Heating, Refrigerating and Air ConditioningEngineers (ASHRAE). Just a few organisms can be transmitted from the reservoirto a niche where they can grow to high levels. Examples of these amplifiers arehumidifiers, 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 oflegionellae can become an amplifier.

According to an ASHRAE position paper, "Legionellae are carried in thetreated drinking water to buildings where they enter and colonize the plumbingfixtures, especially of the domestic hot water system. Cooling towers and otherwet-type-heat rejection systems also can become colonized if potable watercontaining legionellae (at very low numbers) is used as the source for theirmake-up water. This is probably the most frequent way equipment becomescontaminated even though some equipment--such as cooling towers--are excellentair scrubbers. Aerosolized legionellae contained in droplets may possibly beremoved from the air and find a niche in open recirculating systems."

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

ASHRAE believes that if legionellae are prevented from amplifying in or on adevice, the probability of having legionellae in sufficient concentrations to beinfectious to a susceptible host is significantly reduced. The organizationsuggestions the following strategies for minimizing colonization and/oramplification 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 doingthe 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.