Legionnaires disease associated with potable water in a hotel—Ocean City, Maryland, October 2003-February 2004

Morbidity and Mortality Weekly Report, Feb 25, 2005 by D. Goeller, D. Blythe, M. Davenport, M. Blackburn, B. Flannery, C. Lucas, B. Fields, M. Moore, A.D. Castel, L. Hicks

During October 2003-February 2004, eight cases (seven confirmed cases and one possible) of Legionnaires disease (LD) were identified among guests at a hotel in Ocean City, Maryland. This report summarizes the subsequent investigation conducted by the Worcester County Health Department (WCHD), Maryland Department of Health and Mental Hygiene (DHMH), and CDC, which implicated the potable hot water system of the hotel as the most likely source of infection. The detection of this outbreak underscores the importance of enhanced, state-based surveillance for timely detection of travel-associated LD and implementation of control measures.

On December 1, 2003, a local health department (LHD) notified DHMH of two LD cases in Maryland residents who had stayed at hotel A during the 2-10-day incubation period. The two patients had stays in hotel A of 3 and 4 days; their onsets of illness occurred 8 and 5 days, respectively, after leaving hotel A. Both patients had radiographically confirmed pneumonia and positive Legionella urinary antigen tests that were consistent with L. pneumophila serogroup 1 (Lp1) infection. The two patients had stayed at hotel A within 1 day of each other and were linked epidemiologically through travel information collected by LHDs in Maryland by using the DHMH report form for LD. This form collects information regarding location, accommodations, and dates of travel for the 10 days preceding illness. Review of LD case report forms revealed six additional LD patients with reported travel to Ocean City during the preceding year; however, none had stayed at hotel A.

After environmental inspections and water sampling of hotel A by WCHD, multiple samples from multiple sites in the hotel revealed the presence of Lp1. On January 26, 2004, hotel A attempted remediation by superheating water systems, flushing all water taps, and hyperchlorinating the cooling tower. Showers and faucets were reportedly disinfected, and shower heads and sink aerators were replaced in rooms where patients had stayed.

Case Findings

After the initial cases were identified, enhanced surveillance was conducted, including postings on the CDC (Epidemic Information Exchange (Epi-X) and a rapid review of all DHMH case report forms for LD. In February 2004, two additional LD patients were identified, including one person who had stayed at hotel A after remediation. On the basis of this finding and the potential for ongoing but undetected transmission of Legionella, CDC was invited to join the investigation.

To identify additional cases, neighboring jurisdictions, acute care hospital emergency departments, and all LHDs in Maryland were notified. Press releases and hotel A guest notifications were issued by DHMH, WCHD, and hotel A. Reports of persons with illness after a visit to Ocean City were reviewed by WCHD and DHMH to determine whether criteria for the LD case definition were met. A confirmed case of LD was defined as radiographically confirmed pneumonia with laboratory evidence of Legionella infection in a resident or visitor to Ocean City during October 2003-February 2004, whose illness began within 10 days of time spent in Ocean City. Laboratory confirmation included identification of Legionella by culture, direct fluorescent antibody testing, urine antigen assay, or an increase in antibody titer indicating recent infection. Possible LD cases were defined similarly but without laboratory confirmation of Legionella infection or other infectious etiology.

Enhanced surveillance identified approximately 50 ill persons with exposure to hotel A. Further investigation resulted in identification of three additional confirmed cases and one possible case, for overall totals of seven confirmed and one possible case of LD during October 2003-February 2004 (Figure). The median length of stay at hotel A was 3 nights (range: 1-4 nights). Symptom onset occurred a median of 7.5 days (range: 4-9 days) after leaving hotel A. The median age of the eight patients was 63 years (range: 37-70 years), and six (75%) patients were men. Underlying medical conditions associated with increased risk for LD included smoking (five patients), diabetes (four patients), and an immuno-compromised condition (one patient). Five cases were confirmed by urine antigen testing and two by serology. Seven patients were hospitalized; none died (Table).

A review of possible exposures at hotel A among the patients with confirmed LD revealed that all had showered or bathed in their respective rooms, and one had used the whirlpool spa. Six patients reported exposure to the swimming pool and whirlpool area. No other common sources of exposure linking all cases were identified.

Environmental Investigation

During December 2003-February 2004, WCHD, DHMH, and CDC conducted three environmental inspections and four rounds of water testing at hotel A. The hotel remained open during the inspections and testing. The rooms in which the seven confirmed patients stayed were located in different areas and on different floors of the hotel. During all rounds of testing, water temperatures in multiple locations were in an ideal range for growth and amplification of Legionella (77[degrees]F-108[degrees]F [25[degrees]C-42[degrees]C]). Lp1 was recovered from multiple sites in hotel A, including the hot water storage tank; cooling tower; multiple hot water heaters; and showers and faucets in rooms occupied by patients and well guests. All environmental Lp1 isolates were the same monoclonal antibody type 1,2,5, * (testing for type 6 was not conducted). Despite isolation of Lp1 from sites in hotel A, cultured isolates from patients were not available to link with environmental isolates through use of monoclonal antibody testing.