Water systems may be inspected (see Section 7) and tested (see Section 8) for legionella under three circumstances (1) in the absence of reported legionellosis (see 5.2); (2) when a single legionellosis case has been reported (see 5.3); and (3) when two or more legionellosis cases are reported in a limited time period and geographic region (see 5.4). Following are factors building owners and operators need to understand when considering testing water systems for legionella in the absence of illness (see 5.2) and for single legionellosis cases (see 5.3). Refer also to the CDC 2003 Guidelines for Preventing Health-Care Associated Pneumonia, and the CDC 2000 Guidelines for Preventing Opportunistic Infections Among Hematopoietic Stem Cell Transplant Recipients, and the WHO Legionella and the Prevention of Legionellosis. Detection of legionella in a water system is not sufficient to identify the system as a health hazard. However, failure to detect legionella does not indicate, conclusively, that the bacterium is not present (see 6.2.4) or that the water system may not pose a potential health hazard. Methods to detect legionella vary in sensitivity and specificity (see 6.2), and laboratories vary in their skill and experience in the isolation and identification of legionella. Isolation of apparently identical legionellae from clinical and environmental samples (see 6.2.1, 6.6.2.4, and Section 8) may suggest that a water system was the source of the legionella responsible for a patient''s infection (see 5.3.2). However, cases of Legionnaires'' disease due to different legionella serogroups or species need not necessarily have different sources of exposure because a system may be contaminated by more than one legionella. Timely inspection, testing, and treatment of possible legionella sources may reduce legal liabilities for facility owners and operators. Refer also to the APHA Public Health Law Manual.
Environmental Testing for Legionella in the Absence of Illness:
Concerned employers, building owners and operators, facility managers, and others seek to prevent real and potential health hazards, if possible. Water system operators may identify undesirable situations by monitoring routinely for legionella and may be able to implement control measures before the bacterium reaches an amount sufficient to cause human illness (see 6.2.4.2). The CDC 2000 Guidelines for Preventing Opportunistic Infections Among Hematopoietic Stem Cell Transplant Recipients advises that because transplant recipients are at much higher risk for disease and death from legionellosis compared with other hospitalized persons, periodic culturing for legionella in water samples from a center''s potable water supply could be regarded as part of an overall strategy for the prevention of Legionnaires'' disease in transplant centers and other facilities housing persons at high risk of infection if exposed (see 6.4.2). There is some evidence that environmental legionella surveillance should be considered a proactive strategy for the prevention of hospital-acquired Legionnaires’ disease (1). However, the optimal methodology (that is, frequency or number of sites) for environmental surveillance cultures in transplant centers has not been determined, and the cost-effectiveness of such a strategy has not been evaluated for either transplant centers or other health-care settings nor for institutional, commercial, or residential buildings.
Some experts advise against testing water systems for legionella in the absence of illness, particularly in buildings other than hospitals or health-care facilities, given that absolute exclusion of this bacterium from water systems may not be necessary to prevent legionellosis nor may it be achiev.......
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