Travel-associated Legionnaires Disease Outbreak among EU Travelers, Phuket, Thailand, December 2006 to January 2007: Role of Environmental Investigation

Abstract

Background: On 10th January 2006, the British Embassy notified the Ministry of Public Health (MOPH) of 4 cases of Legionnaire's Disease (LD) among travelers who stayed at the same hotel in Phuket. On 11st January 2007, we initiated an investigation to determine the magnitude, source and risk factors of the outbreak.
Methods: Using the LD case definition of European Working Group for Legionella Infections (EWGLI), case finding was done at all hospitals in Phuket. Information on each hotel guest from 17th November 2006 to 11st January 2007 was provided to home country officials. We collected water specimens from rooms, common areas and cooling towers from the hotel for legionella culture. A cross-sectional study was conducted among hotel staff, including testing for Legionella pneumophila antibody by indirect fluorescent antibody (IFA) technique to identify risk factors among hotel workers.
Results: Total 5 confirmed cases and 1 presumptive case were detected among all Scandinavians staying at the hotel. In 2004, this hotel was closed for 6 months following the tsunami. During high season, the hotel with 307 rooms supplemented water by buying non-chlorinated water from a local vendor. Water specimens from the hotel had no detectable chlorine and heat pumps were set to only 45oC. Water specimens from rooms and common areas (but not cooling towers) yielded Legionella isolates (L. bozemanii and L. pneumophila serogroup 1). Six hundred and forty five guests were traced, with one-third from the EU. No additional cases were reported. Among the hotel staff, 66.1% had positive titer. Three staff were identified as Pontiac fever. Showering in the hotel (Prevalence Ratio =1.3, 95% CI=1.0-1.7) and people aged more than 45 years (PR=1.4, 95%CI=1.0-1.7) increased risk for Legionella spp. infection.
Conclusions: Non-chlorinated water caused this outbreak. The mode of transmission was more likely direct contact than air-borne because of the low attack rate. Hyperchlorination and disinfection were implemented in the hotel and hot water temperature was increased. Repeated cultures for legionella were negative. The MOPH and provincial staff initiated sentinel Legionella surveillance at two hospitals in Phuket.