Assessing risk of health care-acquired Legionnaires' disease from environmental sampling: the limits of using a strict percent positivity approach.

Background: Elevated percent positivity (≥30%) of Legionella in hospital domestic water systems has been suggested as a metric for assessing the risk of health care-acquired Legionnaires' disease (LD).

Methods: We examined the validity of this metric by analyzing data from peer-reviewed studies containing reports of Legionella prevalence in hospital water (ie, percent positivity) and temporally matched reports of patients with health care-acquired LD.

Results: Our literature review identified 31 peer-reviewed publications reporting matched data.