Report: Household Devices That Retain Warm Water Present Legionella Concerns

A case of Legionnaires’ disease in an infant with an immunocompromising condition highlights the potential health risks of household devices that retain warm water, as explained in a recent issue of CDC’s Morbidity and Mortality Weekly Report (MMWR). In November 2025, a 10-month-old was hospitalized with fever, chest retractions, and abnormal breathing. A few days later, they tested positive for Legionella pneumophila via a microbial cell–free DNA blood test. About a week after that, the results of an L. pneumophila serogroup 1 urinary antigen test also returned positive. According to MMWR, cases of Legionnaires’ disease in infants and children are rare.

The infant had been admitted to the hospital a month earlier to be treated for a condition called juvenile idiopathic arthritis macrophage activation syndrome, then was discharged with immunosuppressant medications. They had also recently consumed formula prepared using a powdered infant formula mixing device. Due to the infant’s recent hospitalization, investigators examined both potential healthcare and household sources.

Though routine water testing at the hospital did not detect Legionella bacteria or abnormal chlorine values, the report states that the hospital cannot be excluded as a source. At home, water collected from both the internal reservoir of a powdered formula preparation device and from the kitchen faucet, which had an under-sink filtration system that removed chlorine, was positive for L. pneumophila serogroup 1. 

“The internal device reservoir contained water at 106°F (41°C); the parents reported they had not fully emptied and drained the device in [more than] 30 days, conditions conducive to Legionella species amplification,” the report explains. It also states that the “removal of chlorine by the filter could have contributed to the growth of Legionella.”

The report urges manufacturers of infant formula mixing devices to consider revising their instructions to focus on routine reservoir maintenance, as the instructions for the device in this case did not specifically call for the internal reservoir to be routinely drained. 

The full report can be accessed from CDC’s MMWR.

Related: Read “Legionella Regulations in New York: How Much Progress Have We Made?” and “Why Legionnaires’ Disease Outbreaks Continue” in the digital Synergist.