Background: The second largest outbreak of Legionnaires' disease in United States history began in July, 2015 in Bronx County, NY. It was initially described as a single outbreak affecting 138 patients with 16 deaths. Subsequently, additional cases were noted in the same area and time period, officially attributed to different exposures, making the final total 155 patients and 17 deaths before ending in September, 2015. The largest portion of cases was seen at Lincoln Medical and Mental Health Center with 48 patients treated. Methods: We reviewed the hospital and public health timeline regarding the official response to the outbreak and performed performed a study of all patients who presented to Lincoln Medical and Mental Health Center from July 8 to August 03, 2015 with laboratory confirmed Legionella infection. The overall mortality was evaluated as well as risk factors for disease and clinical presentation. Results: The standard use of Legionella urine antigen testing for community acquired pneumonia allowed for early identification of the outbreak prior to public health notification. The type of public health service investigations varied by location due to non-uniform application of Centers for Disease Control guidelines. Of the 48 patients with laboratory confirmed disease, median age was 55 years. Patients presented most commonly with tachycardia (88%), fever (79%), and cough (79%). The most common clinical findings were hyponatremia (52%), rhabdomyolysis (42%) and respiratory failure (31%). Antibiotic therapy was initiated within 6 hours for 31 of 48 (65%) patients. Two patients (4%) died during this outbreak. Conclusions: Divergence from Centers for Disease Control guidelines may have limited the investigators' abilities to more accurately determine the sources for the outbreak and may have prevented this from being seen as one rolling epidemic instead of three separate events. Standard use of Legionella urine antigen testing in community acquired pneumonia by Lincoln Medical and Mental Health Center allowed for identification of the outbreak prior to the public health authorities and neighboring hospitals. Rapid diagnosis and prompt treatment led to an overall mortality of 4%.