BACKGROUND: Clinical surveillance of legionellosis cases and environmental surveillance of potential sources of Legionella bacteria are necessary to limit the occurrence of community-acquired and healthcare-associated cases. Perturbations in the distribution system of a public water system such as water main breaks, increased flow from fire fighting activity, water main repair and replacement may either introduce microbial contaminants and/or alter water quality conditions and could favor the subsequent amplification of microorganisms and contribute to increases in the incidence of waterborne illness. Understanding the impact of water supply upset events on the occurrence of waterborne illness, such as legionellosis, is needed in order to inform and provide guidance to stakeholders about the potential health risks, preparedness steps and recovery measures relating to these events.
METHODS: Associations between water supply upset events and legionellosis cases were assessed through retrospective temporal and spatial analysis of public water system emergency events and legionellosis cases reported to NYS DOH in 2001-2016.
RESULTS: Retrospective temporal and spatial analysis revealed inconclusive associations between water supply upset events and legionellosis cases reported to NYS DOH in 2001-2016. On crude analysis, legionellosis case reports peaked in the Summer months, while emergency event reports peaked in the Spring months, with the exception of two years that included large hurricane events. In addition, counties containing the largest urban areas in NY state, which ranked highest in reports of legionellosis cases, ranked relatively low in reports of emergency events.
CONCLUSIONS: An association between water supply upset events and legionellosis incidence, if present, may be masked by surveillance artifacts, changes in reporting system and/or bias in reporting of emergency events by different counties, and may be confounded by other factors, such as seasonal temperature changes and the presence of cooling towers, complex distribution systems and other man-made equipment that can amplify and aerosolize Legionella. Prospective surveillance of legionellosis cases following water supply upset events, starting in 2016, will be conducted in order to clarify the association between these events and outbreaks of legionellosis. In addition, data on water supply changes due to water treatment plant operation, general construction, water infrastructure repair and fire control will be analyzed as to their possible influence on large outbreaks of legionellosis in 2015 and 2016. Classification of new legionellosis cases as probably related to a water supply upset event must eliminate alternative sources of Legionella, such as amplification of residual amounts of bacteria in man-made equipment.