CDC Report on U.S. Drinking Water Contamination Warns Legionella Outbreaks Increasing

A new analysis of waterborne diseases conducted by federal health officials reveals that harmful pathogens found in biofilms, such as legionella and nontuberculous mycobacteria (NTM), are the leading causes of waterborne disease outbreaks in the U.S.

In a Morbidity and Mortality Weekly Report released this week, the U.S. Centers for Disease Control and Prevention (CDC) indicate that waterborne pathogens are responsible for approximately 7.15 million illnesses, 118,000 hospitalizations, and 6,630 deaths each year in the United States. The report links Legionella and NTM exposure to 40% of water contamination-related hospitalizations, and 50% of waterborne disease deaths.

The CDC reviewed drinking water outbreak data reported from 28 states between 2015 and 2020, finding that 87% were associated with pathogen biofilms, and 80% involved contaminated water from public water systems.

Legionella was associated with 98% of biofilm-related outbreaks, and was responsible for 92% of public water system outbreaks, 97% of hospitalizations, and 98% of deaths. The report also linked legionella to 98% of biofilm-related outbreaks in health care facilities, which resulted in 65% of hospitalizations and 85% of deaths reported during the study period.

Drinking Water Pathogens

Biofilms grow in water lines and on other moist surfaces when taps are not turned on for extended periods, or when water is not properly disinfected, allowing stagnant water to accumulate a glue-like mixture of bacteria, fungi, amoebas and other potentially harmful microorganisms. Once biofilms form, pathogens, including legionella bacteria, are difficult to control because they are resistant to water purification treatments.

Legionella bacteria infects the lungs when an individual breathes in contaminated water droplets or swallows contaminated water. Exposure can result in a serious type of pneumonia, known as Legionnaire’s disease. Nearly 10% die from complications and 25% of those deaths are reported in health care settings, like nursing homes.

The CDC report indicates that most of the waterborne outbreaks reported between 2015 and 2020 involved legionella bacteria, and inadequate water disinfection was the primary contributing factor.

Officials observed an increasing trend of legionella-related outbreaks, with numbers rising nearly every year during the study period. They indicate legionella outbreaks have become the major cause of hospitalizations and deaths associated with waterborne and drinking water diseases.

The findings highlight the need for improved water treatment procedures, the CDC indicates. Public health and drinking water regulators should use the report’s findings to identify waterborne disease threats and develop outbreak response and prevention programs.