A Large Community Outbreak of Legionnaires' Disease Associated With a Cooling Tower in New York City, 2015

Abstract

Objectives: Infections caused by Legionella are the leading cause of waterborne disease outbreaks in the United States. We investigated a large outbreak of Legionnaires' disease in New York City in summer 2015 to characterize patients, risk factors for mortality, and environmental exposures.

Methods: We defined cases as patients with pneumonia and laboratory evidence of Legionella infection from July 2 through August 3, 2015, and with a history of residing in or visiting 1 of several South Bronx neighborhoods of New York City. We describe the epidemiologic, environmental, and laboratory investigation that identified the source of the outbreak.

Results: We identified 138 patients with outbreak-related Legionnaires' disease, 16 of whom died. The median age of patients was 55. A total of 107 patients had a chronic health condition, including 43 with diabetes, 40 with alcoholism, and 24 with HIV infection. We tested 55 cooling towers for Legionella, and 2 had a strain indistinguishable by pulsed-field gel electrophoresis from 26 patient isolates. Whole-genome sequencing and epidemiologic evidence implicated 1 cooling tower as the source of the outbreak.

Conclusions: A large outbreak of Legionnaires' disease caused by a cooling tower occurred in a medically vulnerable community. The outbreak prompted enactment of a new city law on the operation and maintenance of cooling towers. Ongoing surveillance and evaluation of cooling tower process controls will determine if the new law reduces the incidence of Legionnaires' disease in New York City.

Keywords: Legionnaires’ disease; cooling tower; outbreak.

Figure 1.

Outbreak of Legionnaires’ disease, by date, South Bronx, New York City, July 2 to August 3, 2015 (n = 132). The date of illness onset was obtained from patient interviews and was missing for 6 patients who were unable or refused to be interviewed.

Figure 2.

Emergency department (ED) visits for pneumonia syndrome in the Bronx and Legionnaires’ disease outbreak zone, New York City, July 1 to October 7, 2015. Keywords included pneumonia, Legionella, Legionnaires’ disease; International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes 480-486.

Figure 3.

Crude attack rates of Legionnaires’ disease by census tract and cooling towers testing positive for Legionella pneumophila serogroup 1 (Lp1), Bronx, New York City, July 2 to August 3, 2015. Circles indicate buildings with cooling towers in which Lp1 was isolated. All buildings have 1 cooling tower except for building F, which has 2 cooling towers. DNA subtyping performed through pulsed-field gel electrophoresis: olive circles indicate buildings with cooling towers having the O-1 strain, which was indistinguishable from 26 patient isolates; white circles indicate buildings with cooling towers that had non–O-1 strains (ie, not related to patient isolates). Abbreviation: PFGE, pulsed-field gel electrophoresis.

Figure 4.

Molecular subtyping of outbreak-associated Legionella pneumophila serogroup 1 patients and environmental isolates, Bronx, New York City, 2015. Pulsed-field gel electrophoresis (PFGE) with restriction enzyme Streptomyces fimbriatus (Sfi I). Lane 1 is a representative human isolate, and lanes 2 to 15 are the 14 cooling tower isolates from the South Bronx outbreak zone.