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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-
to 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.
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. 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 immunocompromised condition (one patient). Five cases were confirmed by
urine antigen testing and two by serology. Seven patients were hospitalized;
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
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°F–108°F [25°C–42°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.
After the third and fourth cases of LD were identified, a second superheating
remediation was conducted at hotel A in February 2004. In addition, shower
necks and faucets in all hotel rooms and condominiums were reportedly disinfected
with a bleach solution. The whirlpool spa sand filter was cleaned. In March
2004, given the apparent inadequacy of the initial remediation, the potable
water system was hyperchlorinated, and a postremediation plan for water testing
for Legionella was instituted. Since the hyperchlorination
treatment, no further cases of LD associated with hotel A have been identified.
During postremediation follow-up testing, one Lp1 isolate from the cooling
tower was identified at a low level, and the cooling tower was hyperchlorinated.
DHMH continues to monitor for additional cases associated with hotel A and
for all travel-associated LD cases.
Reported by: D Goeller, MS, Worcester County
Health Dept, Snow Hill; D Blythe, MD, M Davenport, MD, M Blackburn, MPH, Maryland
Dept of Health and Mental Hygiene. B Flannery, PhD, C Lucas, PhD, B Fields,
PhD, M Moore, MD, Div of Bacterial and Mycotic Diseases, National Center for
Infectious Diseases; AD Castel, MD, L Hicks, DO, EIS officers, CDC.
CDC Editorial Note: Hotels have been common
locations for LD outbreaks since the disease was first recognized among hotel
guests in Philadelphia in 1976.1,2 In this report, the exposure
of patients to the hotel’s potable water system, the lack of other epidemiologic
links, and the recovery of Legionellae from multiple
points in the system suggest that the hotel potable water system was the source
of the outbreak. Approximately 8 million visitors travel to Ocean City each
year; therefore, a link between the first two cases was not immediately evident.
Available data were searched to identify additional cases associated with
the hotel or travel to Ocean City. Active surveillance activities led to more
rapid identification of other cases. The retrospective identification of these
cases prompted further investigation and subsequent control and remediation
efforts at hotel A.
In 2003, DHMH began conducting enhanced surveillance because of increased
reports of LD. All patients reported to DHMH are administered a follow-up
questionnaire by local or state health departments. The questionnaire identifies
travel that preceded the illness, including location, accommodations, dates,
and information about exposures to common sources for infection, such as whirlpool
spas and cooling towers.
Surveillance data submitted to CDC indicate that approximately 21% of
LD cases each year are travel associated.3 However, several factors
hinder identification of travel-associated clusters of the disease. The LD
incubation period is long enough for persons to disperse from the point source
of infection. In addition, LD can be treated successfully with empiric antibiotics,
which obviates the need for confirmatory testing. When diagnostic testing
is performed, isolation of the organism is rare, preventing comparison of
environmental isolates with clinical isolates.
Improved national surveillance for travel-associated LD might help detect
clusters of the disease. Surveillance for LD in the United States consists
of two systems, a national, paper-based system and an electronic system reported
through the National Electronic Telecommunications System for Surveillance.
Only the paper case-report form collects information on location of travel
and lodging. Although the paper case-report form is useful for tracking overall
trends, a lack of timeliness and sensitivity, often resulting in an inability
to link cases, limits its usefulness in identifying clusters.4
The European Working Group for Legionella Infections, established in
1986, has developed a successful surveillance system for identifying clusters
of travel-associated LD. The European Surveillance Scheme for Travel-Associated
Legionnaires Disease, which consists of 36 collaborating countries, compiles
case data electronically and cross-checks travel accommodations with other
cases to identify clusters. During 2000-2002, a total of 113 travel-associated
LD clusters were reported, with the majority linked to hotels. Since introduction
of the European group’s guidelines in July 2002, all LD clusters are
investigated, and remediation and control measures are instituted when necessary.5,6
The European and DHMH programs demonstrate how timely, sensitive surveillance
can identify clusters of travel-associated LD. Prompt recognition and investigation
of clusters can implicate a point source for infection and guide remediation
and control efforts. Recognizing the benefits of enhanced surveillance, CDC
plans to work with state health departments on new strategies to improve surveillance
for travel-associated LD at the national, state, and local levels.
The findings in this report are based, in part, on contributions by
R Thompson, P Dietrich, Baltimore County Health Dept, Baltimore; R Shockley,
D Stevens, E Potetz, K Malloy, T Possident, Worcester County Health Dept,
Snow Hill, Maryland. J Li, Office of Workforce and Career Development, CDC.
References: 6 available
Legionnaires Disease Associated with Potable Water in a Hotel—Ocean City, Maryland, October 2003–February 2004. JAMA. 2005;293(13):1584–1585. doi:10.1001/jama.293.13.1584