Between 28 April and 9 May, 34 grouped cases of Legionnaire’s disease were recorded in a sector covering 20 km: 26 cases in the Rhône department, and 6 in the Ain. The national network identified two other cases: these individuals resided in the Isère and Côtes d’Armor departments and all shared having visited a zone located between Caluire and Rillieux-la-Pape. Environmental investigations were carried out at the victim’s homes. Physicians in the affected sector were asked to remain on the lookout for any characteristic clinical signs.
The Prefecture ordered the following precautionary measures: cleaning and disinfection of air cooling towers in service; suspension of operations for all newly built air cooling towers; ban on in-store spraying of fresh produce; prohibition of operating car washes; cessation of water jets and waterfalls running in a closed circuit within Caluire and Rillieux; and the requirement of all vegetable and flower growers to disinfect their irrigation network and use potable water.
A flyover of the region in a helicopter equipped with photographic instruments and a thermal camera made it possible to locate 16 sites capable of housing an air cooling tower and then verify the actual shutdown of the tower targeted by administrative order. A field investigation found that 12 sites had not yet declared their towers. Provided they had been cleaned and disinfected, water jets, waterfalls and car washes were authorised to restart operations. On 1st June, air cooling towers at 28 sites had been controlled: 11 had been turned off since autumn 2004, yet with 1 disinfection to be performed; another 11 were removed from suspicion following analyses; and for the other 5, analyses revealed the presence of Legionnaire’s disease. The environmental strains however did not correspond to the human strains. For 1 site, analytical results were still outstanding. The sprayers at 3 stores, irrigation systems and the 7 car washes were all eliminated as potential contamination sources as their analytical results proved negative. All non-contaminated installations were authorised to resume activities, provided that managers committed to conducting more stringent inspections. A comparison between the pneumophila serogroup type 1 strain (so-called Lorraine strain), identified in 3 patients, and the environmental strains has not yet enabled identifying the source of contamination.