Advice for culturing water for legionella
The Allegheny County Health Department in Pittsburgh recommends that water culturing for legionella should be done at least annually, more often in hospitals with high-risk patients like organ transplant recipients.1 In-house or reference laboratory testing capabilities also are recommended to identify cases in patients. (See charts, pp. 75-76.)
In hospitals of less than 500 beds, a minimum of 10 distal sites should be surveyed. Larger hospitals should culture two distal sites per 100 beds. The sites should be taken from units housing patients at higher risk for acquiring Legionnaires' disease. Small numbers of legionella species in a limited number of distal sites will not pose unusual danger for hospitalized patients if a strong infection control program utilizing in-house laboratory capability is present.
If any single water tank or site is positive for a legionella species, then specialized laboratory testing for legionella should be available, either in-house or through a reference laboratory, for patients with nosocomial pneumonia. If the percent of positive cultures at the distal sites is 30% or more of the total number sampled, then disinfection of the water distribution system is appropriate. Environmental cultures confirming efficacy should be considered after disinfection.
If the rate of positive cultures is less than 30%, disinfection measures need not be initiated until definition of the problem is clarified. However, prospective surveillance by legionella laboratory testing for all patients with nosocomial pneumonia becomes important. The infection control practitioner and a physician should take responsibility for ensuring that such patients have the appropriate tests ordered. Culture of respiratory tract specimens on selective media, direct fluorescent antibody stain, urinary antigen, and acute and convalescent serology are appropriate. If there are a significant number of immunosuppressed patients, then in-house capability for the legionella laboratory tests is appropriate.
To conduct a water culture survey, the Allegheny guidelines recommend the following:
Faucets: Moisten the outlet by allowing water to trickle through the opening. A sterile, dacron swab should be inserted and rotated four times around the inner circumference, moving up the faucet as far as the swab will reach. Place the swab into the container. If the swab system does not contain a transport medium, then allow 0.5 ml of water to flow from the faucet into the container to keep the swab moist. If the culture system has a self-contained transport medium, it is not necessary to add outlet water to the swabs.
Showerheads: Moisten the showerhead by allowing water to trickle through the opening. Rotate the swab over the entire surface of the showerhead four times. Place swab into the container. If the swab system does not contain a transport medium, then allow 0.5 ml of water to flow from the showerhead into the container to keep the swab moist.
Hot water tanks: Open the drain valve at the base of the tank. Collect 10 to 50 cc immediately into a sterile specimen container. Let the water drain out of the pipe for 15 to 30 seconds to flush out residual water within the drain pipe, and then collect another 10 to 50 cc into a second specimen container. This procedure ensures that both residual water in the drain pipe and water from the tank are sampled.
(Editor's note: For information about obtaining a copy of the complete guidelines, contact the Allegheny County Health Department, 3333 Forbes Ave., Pittsburgh, PA 15213.)
Reference
1. Allegheny County Health Department. Approaches to Prevention and Control of Legionella Infection in Allegheny County Health Care Facilities. Pittsburgh; 1993. *
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