<i>Legionella</i> DNA Markers in Tap Water Coincident with a Spike in Legionnaires’ Disease in Flint, MI

Abstract

Two clusters of Legionnaires' disease occurred in Flint, MI, subsequent to switching to a corrosive potable water source from April 2014 to October 2015. We hypothesized that the interrupted corrosion control and associated release of iron, nutrients, and depleted chlorine residual in the distribution system would lead to high levels of Legionella. A tap water survey conducted throughout Flint in August and October 2015 confirmed Legionella pneumophila in two hospitals (mean of 1890 ± 2220 gene copy numbers/mL, 48% positivity), but not small single-story buildings. The hospitals frequently had optimal Legionella growth temperatures and were located in high-water age zones of the distribution system (3 to >6 days). Relatively high concentrations of iron were present (mean of 51.0 ± 37.2 ppb), and Cl2 residual was sporadic (mean of 0.700 ± 0.775 mg/L) throughout the Flint distribution system. This study addresses knowledge gaps linking legionellosis outbreaks to changes in municipal water quality and distribution system operation.