On Fri 27 Jul 2007 the Department of Communicable Disease Control and Prevention, Stockholm County Council was informed by one of the infectious diseases hospitals in Stockholm, Sweden, that 3 females from a cruise ship had been hospitalised due to severe pneumonia. The chest X-rays from each of them showed bilateral infiltrates. Based on this information the Stockholm Environmental Health Office was asked to make contact with the ship.
 
This contact was established and the ship was offered help with sampling for _Legionella_ bacteria from the environment on the ship. A total of 13 water samples and 5 swabs samples were collected during the same day. It was later revealed that 2 more persons were hospitalised in another infectious diseases hospital in Stockholm. One had X-ray verified pneumonia and the other had an exacerbation of COPD [chronic obstructive pulmonary disease], but no pulmonary infiltrates on chest X-ray. Both were discharged on 30 Jul 2007.
 
The cruise ship left Stockholm on Saturday morning 28 Jul 2007 and returned directly to Dover, UK. More actions have been taken in the UK. Urinary antigen tests from one of the 4 pneumonia patients showed a borderline positive result. PCR on sputum samples from 2 of the 4 were positive for _Legionella_, one whom also had the borderline
positive urinary antigen test.
 
The water samples showed very low amounts of _L. pneumophila_ (10 cfu/L) and no _Legionella_ bacteria were detected in the swab samples. However the final laboratory results will be available next week [6-10 Aug 2007].
 
To conclude there were 4 persons with clinical and radiological symptoms compatible with legionellosis. Of those 4, 2 had PCR positive sputum for _Legionella_, one of whom also had a positive urinary antigen test. All 4 responded rapidly to treatment directed against Legionella. Taken together with the fact that _L, pneumophila_ were detected in low amounts in water samples from the cruise ship it indicates that transmission of _Legionella_ may have occurred in the ship. Further microbiological analyses are needed to confirm this suspicion.
 
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