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Chapter 70 : Outbreak of Legionnaires' Disease Linked to a Humidifier in a Hotel in Wales, United Kingdom
Ten cases of indigenously acquired Legionnaires' disease were identified by routine laboratory surveillance in Wales, United Kingdom, over a period of 7 months. Epidemiological investigations started with a case-control study. Case definitions used were those of the European Working Group for Legionella Infections; controls were taken from people who accompanied the three patients who had visited the hotel as part of a group. A cohort study was designed with staff who worked during the weekend that two patients had visited the hotel. The hypothesis was that more seroconversions would have occurred among people working close to the source, so that the average titer in this group would be higher than in people not exposed to the source. Six patients had a lung infiltrate on chest X ray. The first patient visited the hotel in July 1999, patients 2 and 3 visited in December 1999, patients 4 and 5 visited in January 2000, and patient 6 visited in February 2000. Only one stayed overnight and dined in the hotel, one used the swimming pool and spa for a week, three attended a lunch, and one attended an evening meal. Three of six patients were active smokers; none were immunosuppressed. Neither the case-control study nor the cohort study indicated a possible source of infection. Public Health officials and local authorities were notified of the possible role of ultrasonic humidifiers in the transmission of legionellae.