March 14, 2024

CDC Report Characterizes Waterborne Disease Outbreaks

From 2015 through 2020, Legionella was responsible for 97 percent of hospitalizations and 98 percent of deaths resulting from reported waterborne disease outbreaks in the United States, according to a new report from CDC. Based on information provided by 28 states, the report categorizes outbreaks as either enteric or associated with biofilm pathogens, identifies contributing factors, and describes the settings where outbreaks occurred.

Of the 214 total outbreaks reported by public health officials during the study period, 187 were associated with biofilm, 24 with enteric illness, and one with a chemical or toxin. Two outbreaks had unknown causes.

Legionella was the culprit in nearly all the biofilm-related outbreaks. Two involved nontuberculous mycobacteria (NTM) and one Pseudomonas. Since NTM infections are not nationally notifiable diseases, their numbers could be underreported, according to CDC.

The number of Legionella-associated outbreaks jumped from 14 in 2015 to 31 the following year, growing to 34 in 2018 and dropping to 18 in 2020. The report states that the COVID-19 pandemic may have affected reporting in 2020.

Although responsible for nearly all severe outcomes, Legionella caused only 37 percent of illnesses from reported waterborne disease outbreaks. Enteric illnesses accounted for 61 percent of illnesses but only 2 percent of hospitalizations and no deaths. The vast majority of reported enteric illnesses were caused by norovirus, Shigella, or Campylobacter.

More than half of the 214 outbreaks during the study period occurred in healthcare facilities, by far the most common setting. All outbreaks in healthcare facilities were biofilm related. Other settings with large numbers of outbreaks included hotels, motels, and similar lodging facilities.

For more information, read “Surveillance of Waterborne Disease Outbreaks Associated with Drinking Water — United States, 2015–2020” in the March 14 issue of Morbidity and Mortality Weekly Report.

Related: Read “Performing Legionella Source Risk Assessments: A Hazard Analysis Tool for Data Interpretation” in the April 2019 Synergist.