By Ethan Covey

Legionnaires disease was identified in an immunocompromised infant who had recently consumed powdered formula prepared with filtered tap water and mixed by a home formula preparation device, according to a recently released report (MMWR Morb Mortal Wkly Rep 2026;75[23]:297-299).

Legionella pneumophilia. Source: CDC/Public Domain.

What Happened?

The case involved a 10-month-old female infant who was admitted to Georgetown University Hospital, in Washington, D.C., in November 2025 with fever, tachypnea, and chest retractions. The infant had recently been hospitalized for treatment of systemic-onset juvenile idiopathic arthritis macrophage activation syndrome and had been discharged on immunosuppressant medications.

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Clinical testing was initially negative for multiple pathogens, but a chest radiograph showed left upper lobe consolidation. A microbial cell-free DNA blood test later detected Legionella pneumophila, and a urinary antigen test was positive for L. pneumophila serogroup 1. The infant recovered following treatment.

How Did the Infant Get Infected?

Because the infant had had both recent healthcare exposures and household exposures during the Legionnaires disease incubation period, investigators evaluated possible sources of the infection. Routine hospital water testing did not detect Legionella bacteria or abnormal chlorine values, although the facility could not be excluded as a source.

The infant’s primary potential household exposure was formula prepared using a powdered infant formula mixing device. Water from the device’s internal reservoir tested positive for L. pneumophila serogroup 1 at a higher concentration than water collected from the kitchen faucet used to fill the device. The faucet had an under-sink filtration system that removed chlorine, and the device reservoir held water at 106°F. The family reported the device had not been fully emptied and drained in more than 30 days.

“Household devices that retain warm water are possible Legionella bacteria sources and might pose a health risk, especially for persons with immunocompromising conditions,” said lead author Eric J. Stern, MD, an associate professor in the Department of Pediatrics and the chief of the Division of Infectious Diseases at Georgetown University Hospital.

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Dr. Stern said ready-to-feed formula may be used for formula-fed infants with immunocompromising conditions. If powdered formula is used, water should be heated to at least 158°F and cooled before feeding.
“Boiling water will kill Legionella organisms if they are present,” he said.

The sources reported no relevant financial disclosures.