28 January 2015 | Commentary

Risk Assessment and Prediction for Healthcare-Associated Legionnaires’ Disease: Percent Distal Site Positivity as a Cut-Point

To date there is no definitive indicator for risk of disease regarding levels of Legionella. In 1983, SPL researchers offered a cut point based on the proportion of outlets (faucets and showers) positive for L. pneumophila. Clinical experience supported this approach. If 30% or greater of outlets was positive for Legionella, environmental and clinical surveillance must be done concurrently; and depending on the extent of colonization consider disinfection. The Allegheny County Health Department was the first to adopt the cut point that public agencies and hospitals now use worldwide.

However, an article published in American Journal of Infection Control (AJIC) challenged this approach. SPL’s editorial commentary, Risk Assessment and Prediction for Healthcare-Associated Legionnaires’ Disease: Percent Distal Site Positivity as a Cut-Point, examines the flaws of that study. That is, researchers applied the 30% criteria to studies not designed to assess this endpoint and therefore the data presented doesn’t prove or disprove the efficacy of the cutpoint.

Commentary Abstract: Legionella has been reported as the single most commonly reported pathogen associated with disease outbreaks from drinking water. Two strategies have been proposed for risk assessment. The first is the strategy advocated by the Centers for Disease Control and Prevention (CDC) to search assiduously for Legionnaires' disease in all cases of hospital-acquired pneumonia. However, the diagnosis is commonly missed, even if the Infectious Diseases Society of America and American Thoracic Society guidelines are followed.