Title : Severe legionella pneumonia case series at an urban academic medical center
Abstract:
An outbreak of Legionnaires’ disease began in New York City in July 2025. In this abstract we present a series of three severe cases of Legionella pneumonia seen in an urban academic emergency department:
Case 1: A 71-year-old male with a history of hypertension, hyperlipidemia, and prior cerebrovascular accident presented to the Emergency Department for decreased level of alertness and slowed, incoherent speech. His initial vital signs were notable for heart rate 150 bpm and oxygen saturation 91% on room air. Laboratory results were notable for acute renal failure, with a creatinine level of 8.7 mg/dL from a baseline of 1, as well as significant transaminitis. Creatine kinase was 69,907 U/L; there was no reported downtime. Chest X-ray showed bibasilar opacities concerning for pneumonia. Urine antigen testing resulted positive for Legionella. The patient was admitted to the Medical Intensive Care Unit (MICU) where he required intermittent hemodialysis.
Case 2: A 38-year-old male with no significant history presented to the ED with five days of nausea, diarrhea, and shortness of breath. Vital signs were notable for heart rate 135 bpm and oxygen saturation 97% on room air. Labs were notable for sodium 122 mmol/L, potassium 2.5 mmol/L. Chest imaging demonstrated right upper lobe consolidation. He became progressively more confused in the ED. Repeat bloodwork showed his sodium acutely declined to 107 mmol/L. Hypertonic saline was initiated in the ED and he was transferred to the MICU, where desmopressin was given for severe hyponatremia secondary to SIADH. Urinary antigen returned positive for Legionella.
Case 3: A 64-year-old male with a history of obesity presented to the ED for a week of diarrhea and dyspnea. His vital signs were notable for heart rate 113 and oxygen saturation of 81% on room air. Cross-sectional imaging demonstrated multifocal pneumonia. He was admitted to the MICU for acute hypoxic respiratory failure requiring escalating settings of non-invasive ventilation. He was consented for extracorporeal membrane oxygenation (ECMO) and cannulated on Day 3 of admission.
Discussion: Legionnaires’ disease is associated with significant morbidity and mortality with nearly half of patients diagnosed with Legionella pneumonia requiring intensive care. Legionella causes infection through inhalation of water droplets contaminated by the bacteria. In the recent outbreak in New York City, Legionella bacteria was released into the air as aerosols from cooling towers in multiple buildings. As global temperatures continue to rise, Legionella, which thrives in warm water, will be a continued public health threat. In our case series, patients ultimately diagnosed with Legionella pneumonia presented to an academic medical center with different chief complaints and had multiple manifestations of the disease.
Chief complaints in our case series included confusion, cough, dyspnea, and diarrhea. Legionella most commonly causes pulmonary and gastrointestinal manifestations but can have multiple extra-pulmonary manifestations as well. One patient in our case series developed rhabdomyolysis secondary to Legionella, which is a rare but serious complication of Legionella secondary to an endotoxin released by Legionella that directly damages muscle tissue. Additionally, one patient developed profound hyponatremia secondary to SIADH, a well-documented but potentially life-threatening complication of Legionella infection. Our cases highlight the importance of recognizing broad laboratory abnormalities as an early clue to Legionella pneumonia,even before respiratory symptoms predominate.
