Prevalence of Infection-Competent Serogroup 6 Legionella pneumophila within Premise Plumbing in Southeast Michigan

Abstract

Coinciding with major changes to its municipal water system, Flint, MI, endured Legionnaires’ disease outbreaks in 2014 and 2015. By sampling premise plumbing in Flint in the fall of 2016, we found that 12% of homes harbored legionellae, a frequency similar to that in residences in neighboring areas. To evaluate the genetic diversity of Legionella pneumophila in Southeast Michigan, we determined the sequence type (ST) and serogroup (SG) of the 18 residential isolates from Flint and Detroit, MI, and the 33 clinical isolates submitted by hospitals in three area counties in 2013 to 2016. Common to one environmental and four clinical samples were strains of L. pneumophila SG1 and ST1, the most prevalent ST worldwide. Among the Flint premise plumbing isolates, 14 of 16 strains were of ST367 and ST461, two closely related SG6 strain types isolated previously from patients and corresponding environmental samples. Each of the representative SG1 clinical strains and SG6 environmental isolates from Southeast Michigan infected and survived within macrophage cultures at least as well as a virulent laboratory strain, as judged by microscopy and by enumerating CFU. Likewise, 72 h after infection, the yield of viable-cell counts increased >100-fold for each of the representative SG1 clinical isolates, Flint premise plumbing SG6 ST367 and -461 isolates, and two Detroit residential isolates. We verified by immunostaining that SG1-specific antibody does not cross-react with the SG6 L. pneumophila environmental strains. Because the widely used urinary antigen diagnostic test does not readily detect non-SG1 L. pneumophila, Legionnaires’ disease caused by SG6 L. pneumophila is likely underreported worldwide.

Comparison of Whole-Genome Sequences ofLegionella pneumophilain Tap Water and in Clinical Strains, Flint, Michigan, USA, 2016

“…Water isolates belonging to serogroup 6, all classified as ST2518, were widespread in samples collected from a Flint hospital in March 2016. A study of L. pneumophila isolates collected from Flint tap water in September and October 2016 also found that serogroup 6 isolates were widespread in residential premise plumbing water samples, although these isolates all belonged to STs 367 and 461 ( 34 ). Byrne and colleagues found that serogroup 6 strains were at least as infectious for macrophages as a known virulent laboratory strain, emphasizing the potential for Legionnaires’ disease to be caused by strains other than serogroup 1 ( 34 ), although more research is needed to confirm the relevance of serogroup 6 strains for human infectivity.…”

The Flint water crisis

“…The water also disrupted the biofilm that forms on the inner surface of pipes, liberating the bacteria that grow there. Combined with persistently low chlorine levels in parts of the water system and the abundance of iron rust offering a ready microbial food supply, this created a situation conducive to bacterial growth (Byrne et al, ; Rhoads et al, ; Schwake, Garner, Strom, Pruden, & Edwards, ; Zahran et al, ). Efforts to counteract bacterial threats led in some instances to overchlorination, resulting in elevated levels of carcinogenic trihalomethanes (THMs) created through the interaction of chlorine and organic matter.…”

Linking Microbial Community Composition in Treated Wastewater with Water Quality in Distribution Systems and Subsequent Health Effects

“…Numerous factors influence the quality of drinking water from large metropolitan areas to the smaller cities. However, one common factor is the water distribution systems which if not managed properly can result in some serious health effects as recently reported in Flint, Michigan, USA [14,15]. Between 2014 and 2015 there was a major outbreak of Legionnaires' disease (LD) in Genesee County, Michigan, and this coincided with changes in the source of drinking water to Flint's municipal water system [14].…”