Did Municipal Water Distribution System Deficiencies Contribute to a Legionnaires' Disease Outbreak in Quincy, IL?

Fifty-eight people were sickened and 12 died from a Legionnaires' disease (LD) outbreak in Quincy, IL, in 2015. The initial outbreak investigation identified deficiencies at the Illinois Veteran's Home (IVHQ), but these did not account for four community-acquired cases that occurred concurrently with no IVHQ exposure. We broaden the investigation to evaluate seven lines of evidence and assess whether municipal drinking water supply deficiencies potentially contributed to a community-wide outbreak. Notably, 3-6 months prior to the outbreak, the primary disinfectant was changed and corrosion control was interrupted, causing a sustained decrease in disinfectant residuals throughout Quincy's distribution system. We hypothesize this created more favorable conditions for Legionella growth throughout the system and an increase in water lead levels. These municipal system deficiencies were not identified in prior investigations of the outbreak, but their impacts on public health outcomes are consistent with those of the 2014-2016 Flint Water Crisis. However, they occurred in Quincy without any legal violations in the municipal water system or public acknowledgment of community-wide health risks. This study supports the critical need for improved data collection during changes in municipal water treatment. Additional regulatory and communication requirements can better protect public health from both LD and lead.