Environmental culturing for Legionella: Can we build a better mouse trap?

Abstract

The drinking water of hospitals has been directly linked to the occurrence of hospital-acquired legionellosis. In addition, the mode of transmission is now known to be primarily aspiration rather than aerosolization. Legionellosis is now recognized as a patient safety concern for nosocomial infection. In 2009, Centers for Medicaid and Medicare Services raised the issue that hospitals might no longer be reimbursed for charges incurred when caring for patientswithhealth care-associated legionellosis based on the argument that this infection is largely preventable. Unfortunately, opposition from the US Centers for Disease Control and Prevention (CDC) and other organizations prevented the measure from passing, but the issue will be revisited next year. Given the direct link between drinking water colonization by Legionella and hospital-acquired legionellosis, national public health agencies have mandated routine environmental surveillance as a preventive measure. On the other hand, some public health agencies, including the CDC, mandate culturing of the hospital drinking water in acute care hospitals only after 1 to 2 cases have been identified. The obvious flaw in this approach is the fact that legionellosis diagnosis requires some index of suspicion. Knowledge that Legionella is within the hospital drinking water raises that index of suspicion. Without this knowledge, hospital-acquired legionellosis has gone undetected to the extent that numerous hospitals have claimed that they have never seen a case of hospital-acquired legionellosis. This commonplace belief has been refuted in numerous prospective studies and most dramatically in Maryland, when hospital-acquired legionellosis abruptly appeared in 2 academic tertiary care health centers in Baltimore within weeks of adopting the Maryland guidelines for proactive surveillance. The table of International Guidelines for Legionella Prevention summarized in the Ditomasso article shows that the guidelines of Australia, France, United Kingdom, and Italy use quantitation (colony-forming units/liter) as a guide for remediation. However, quantitative cultures have not proven to be predictive of the occurrence of hospital-acquired legionellosis. The reasons for this are intuitively obvious. Swabbing of the distal site can remove the biofilm and artifactually affect the quantitation numbers. The biofilm may also be affected by water usage and stagnation. In contrast, the extent of Legionella colonization has proven to be surprisingly robust in predicting the occurrence of hospital-acquired Legionellosis. Extent of colonization is calculated based on the percent distal site positivity (ie, the percent of water faucets that yield Legionella as compared with the total number of cultures taken). Ifmore than 30%of the sampled outlets are positive (especially for Legionella pneumophila), actions should be taken tomitigate the risk to hospitalized patients. Publicity in the newspapers and television complicates the process. In addition, lawsuits based on allegations of negligence have become commonplace for hospitals experiencing nosocomial Legionella infection. A study by the Association for Professionals in Infection Control and Epidemiology-Three Rivers Chapter (TRAPIC) and the Allegheny County (Pittsburgh) Health Department showed that, once proactive surveillance cultures for hospital drinking water were implemented in Pittsburgh, adverse publicity and the incidence of hospital-acquired legionellosis plummeted because preventive measures had been instituted. Ditomasso et al present a sophisticated and comprehensive investigation of a topical issue: improvement of an approach and methodology for performing From the University of Pittsburgh, Pittsburgh, PA; and Special Pathogens Laboratory, Pittsburgh, PA.