A legionellosis case due to contaminated spa water and confirmed by genomic identification in Taiwan

Tracing the source of a legionellosis (LG) case revealed that the Legionella pneumophila (LP) strain isolated from patient's sputum shared the same serogroup (SG) and PFGE-type with 4 LP strains obtained from a spa center. With a high LP-contamination rate (81.2%, 13/16) in all of its 16 basins, this spa center was also found to have a multi-genotypic distribution among its 13 LP isolates, which can be categorized into 5 PFGE-types. Despite such a serious contamination in the spa center, which usually had ca. 100 visitors per day, this male patient, bearing LG-risk factors of long-term heavy smoking and alcoholism, was the only case identifiable after an active investigation. To explore the possible reason for this sporadic infection, all 5 PFGE-types of LP isolated were assayed for their presence of two important virulent genes (lvh and rtx A) and were identified as either less-virulent (lvh (+) , rtx A(+)) or non-virulent (lvh (-), rtx A (-)) types. The strong virulent type (lvh (+), rtx A (+)) usually seen in clinical strains elsewhere was not found here. Moreover, the LG-causative type in this infection was the only one to be classified as the less-virulent type, with the presence of lvh gene indicating its relatively more virulent potential than other 4 PFGE-types. Accordingly, mutual interaction between LP's virulent potential and patient's health-status was suggested to be the force directing the opportunistic infection of this sporadic case. This is the first spa-associated infection caused by SG 2 of LP.