A 10-month-old girl was hospitalized in November 2025 with a fever and difficulty breathing. She had recently been diagnosed with a rare autoinflammatory disease and had been fed formula prepared with a device that mixed powdered formula and warmed water stored in a reservoir.
Testing revealed that both the water in the device and the home environment were contaminated with Legionella pneumophila. This case, detailed in a recent Morbidity and Mortality Weekly Report case study, underscores the risks associated with stagnant warm water.
The report’s authors cautioned that "Household devices that retain warm water are possible Legionella bacteria sources and might pose a health risk, especially for persons with immunocompromising conditions."
Earlier in October 2025, the infant had been admitted to the hospital and diagnosed with systemic-onset juvenile idiopathic arthritis macrophage activation syndrome, a potentially fatal condition causing an overactive immune response. She was treated with immunosuppressant medications and was stable at follow-up appointments.
During her November 17, 2025 visit, lung imaging showed fluid accumulation, and tests confirmed the presence of Legionella pneumophila. She was treated with antibiotics, azithromycin and meropenem, leading to improvement. She was discharged on November 30 with instructions for her parents to administer oral levofloxacin for 21 days.
The infant was readmitted on December 15, with chest scans revealing new lung cavities. As her parents had discontinued using the formula mixer, doctors suspected her ongoing issues were linked to the initial infection. She received a six-day course of azithromycin and was discharged with intravenous antibiotics.
Investigations confirmed the presence of Legionella bacteria in the formula mixing device and the home’s filtered water supply. Although the water filter was not directly tested, the study noted that such filters can become breeding grounds for bacteria if chlorine is removed or if they are not properly maintained.
The study’s authors advise that infants with compromised immune systems should have their formula prepared using water boiled to over 158º Fahrenheit, then mixed and allowed to cool.