Legionnaires' disease (LD) is a severe pneumonia that can be accompanied by gastrointestinal and neurologic symptoms. Risk factors include smoking, age >50 years, and comorbidities. Onset occurs 2-10 days after exposure to Legionella, a genus of intracellular gram-negative bacteria found in water and soil. L. pneumophila serogroup 1 (LP1) causes 65-90% of cases for which there is a bacterial isolate (Bennett, Dolin, & Blaser, 2014). The majority of cases are diagnosed by urine antigen test (UAT), a rapid test that is highly sensitive and highly specific for LP1 and is widely available in acute care settings. Identification of the environmental source relies on comparison of patient isolates and environmental isolates by molecular techniques. Culture of respiratory specimens is necessary to obtain patient isolates, but LD patients might not produce sputum, specimens are not routinely cultured on Legionella-specific media, and specimens are less likely to yield positive culture results if they are collected after a patient has begun antibiotic therapy.
LD outbreaks have occurred from exposure to bioaerosols from cooling towers, decorative fountains, hot tubs, market misting systems, and potable water systems in hospitals, hotels, and residential buildings (Cunha, Burillo, & Bouza, 2016; Fraser et al., 1977; Haupt et al., 2012; Mahoney et al., 1992). Cooling towers have caused large community outbreaks including an outbreak with 334 cases in Portugal in 2014 and an outbreak with 449 confirmed cases in Spain in 2001, and likely have caused many sporadic cases (Bhopal & Fallon, 1991; Garcia-Fulgueiras et al., 2003; Shivaji et ab 2014). Bioaerosols from cooling towers can travel substantial distances and have caused illness among persons up to 11.6 km away from a source (White et al., 2013). Recovery of a bacterial isolate by culture is the standard for identification of Legionella in the environment. PCR can detect Legionella DNA, but does not indicate the presence of viable bacteria or provide a quantitative measure of the degree of contamination.
An estimated 8,000-18,000 cases of LD requiring hospitalization occur annually in the U.S. (Marston et al., 1997). Approximately 200-300 cases are reported annually in New York City; the age-adjusted incidence rate rose from 0.6/100,000 population during 2000 to 2.5/100,000 population during 2014, peaking at 3.4/100,000 population during 2013 (New York City Department of Health and Mental Hygiene [DOHMH], 2015a). This rise might be due to increased use of UAT by healthcare providers, an increase in the population at risk, or changes in the number and maintenance of cooling towers and their colonization by Legionella (Farnham, Alleyne, Cimini, & Balter, 2014). During 2000-2013, Bronx County had between 7-72 cases/year (crude rate 0.5-5.2 cases/100,000 population/year).
Clinical laboratories in New York City report positive Legionella test results to the New York City Department of Health and Mental Hygiene (DOHMH). For each case, DOHMH personnel review medical records to confirm illness and interview the patient or a close relative to determine possible Legionella exposure sources at home, work, healthcare settings, or associated with travel. Identification of a cluster of cases in space and time without a common building exposure indicates an outdoor exposure to a cooling tower or other outdoor aerosol source. An epidemiologist reviews all cases for common exposures and we also detect clusters at the city-, county-, and neighborhood- (multiple ZIP code) levels with a weekly automated system that compares the number of cases diagnosed in the past 4 weeks with that period and the prior and following 4-week periods in the previous 5 years, a modified historical limits method (Levin-Rector, Wilson, Fine, & Greene, 2015).
In December 2014 we identified a cluster of LD cases through a combination of epidemiologist review and automated cluster detection. All cases were located in Co-op City, a 1.3-square-kilometer residential neighborhood in northeastern Bronx County that is home to 60,000 persons, many retired, living in 15,372 residential units, including 14,900 apartments in 35 high-rise towers (24-33 floors) and 472 townhouses in 7 groups. All of Co-op City is contained within ZIP code 10475.
On December 1, 2014, the automated system reported nine cases among persons living in Bronx County (a larger area surrounding Co-op City) over the prior 4 weeks. Review of the four completed interviews found no common building exposures but found that two patients resided in Co-op City. On December 22, the automated system reported 12 cases among persons living in Bronx County over the prior 4 weeks, including four cases in Co-op City. We investigated to determine the magnitude and source, and to prevent further illness.
We defined an outbreak-associated case as LD diagnosed by UAT or culture and radiographic evidence of pneumonia in a person who lived in Co-op City with illness onset during November 2014-January 2015. Initial investigations found no common buildings visited by five patients.
On January 6, 2015, we alerted healthcare providers in New York City about the increase in cases in Bronx County and asked them to collect respiratory tract specimens to culture for Legionella from...