An Infant’s Legionnaires’ Disease Linked to a Formula-Mixing Machine

Legionnaires' disease mostly affects adults over 50; cases in infants are rare. It's usually caught by breathing in contaminated water mist, but aspirating contaminated water can also cause it. This case shows how a home appliance that holds warm water can become a source.

The case

• On November 17, 2025, a 10-month-old girl was admitted to Georgetown University Hospital with fever, rapid breathing and chest retractions.
• She had been hospitalized 32 days earlier with macrophage activation syndrome from systemic-onset juvenile idiopathic arthritis — a life-threatening overactivation of immune cells — and sent home on November 5 on immunosuppressant medicines.
• At home, her formula was made with a powdered infant formula mixing device, which stores water and powder, heats the water to a preset temperature, mixes in the powder and dispenses warm formula.
• Tests for many pathogens were negative, but an X-ray showed left upper lung consolidation. A cell-free DNA blood test detected Legionella pneumophila (November 21), and a urinary antigen test was positive for serogroup 1 (November 28).

Finding the source

Because she'd had health care visits during the 14-day incubation period, both the hospital and home were checked. Routine hospital water testing found no Legionella (though the hospital couldn't be ruled out), and there were no other mist sources such as humidifiers or showers.

The formula device was the main suspect:

• The faucet had an under-sink filter that removed chlorine.
• The reservoir water was 106°F (41°C) — and the parents hadn't fully emptied and drained the device in more than 30 days, conditions that let Legionella multiply. Water stored at 77°F–113°F (25°C–45°C) promotes its growth.

Treatment

She needed oxygen and was treated with azithromycin and meropenem once Legionella was found, then discharged on oral levofloxacin. On December 15 she was readmitted with poor feeding and new cavities in her left lung, despite the family having stopped using the device. Repeat tests again found L. pneumophila, interpreted as the original infection persisting. After more antibiotics and a feeding tube, she went home December 24 to finish IV antibiotics. Her provider reported the device to the Consumer Product Safety Commission in February 2026.

Lessons

• Household devices that keep warm water can harbor Legionella, especially risky for people with weakened immune systems.
• The device maker recommended distilled or boiled water but not routine reservoir draining. Manufacturers could revise designs and instructions to recommend regular reservoir maintenance and stress the risk of unboiled tap water.
• For immunocompromised infants on powdered formula, heat water to at least 158°F (70°C) before mixing (this also guards against other bacteria such as Cronobacter), then cool the formula before feeding. Boiling kills Legionella.
• Poorly maintained water filters may encourage germ growth, and removing chlorine could have helped Legionella grow; the household filter wasn't tested.

Limitations: no clinical and environmental isolates to compare, possible health care exposures during the incubation period, and sampling about two weeks after illness began.

Sources

Based on "Notes from the Field: Case of Legionnaires Disease Associated with a Home Device Used to Mix Powdered Infant Formula — United States, 2025," Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The imported copy was cut off in one place; the missing text was taken from the same report's full text in PubMed Central (PMC13277664).