Legionella spp. Colonization in Water Systems of Hotels Linked with Travel-Associated Legionnaires' Disease

Hotel water systems colonized with Legionella spp. have been the source of travel-associated Legionnaires' disease, and cases, clusters and outbreaks continue to be reported worldwide each year. A total of 132 hotels linked with travel-associated Legionnaires' disease, as reported through the European Legionnaires' Disease Surveillance Network, were inspected and tested for Legionella spp. during 2000-2019 by the public health authorities of the island of Crete (Greece). A total of 3311 samples were collected: 1885 (56.93%) from cold water supply systems, 1387 (41.89%) from hot water supply systems, 37 (1.12%) were swab samples and two (0.06%) were soil. Of those, 685 (20.69%), were collected from 83 (62.89%) hotels, testing positive (>= 50 CFU/L) for Legionella pneumophila) serogroups 1-10, 12-14 and non-pneumophila species (L. anisa, L. erythra, L. tusconensis, L. taurinensis, L. birminghamensis, L. rubrilucens, L. londiniesis, L. oakridgensis, L. santicrusis, L. brunensis, L. maceacherii). The most frequently isolated L. pneumophila serogroups were 1 (27.92%) and 3 (17.08%). Significantly higher isolation rates were obtained from hot water supply systems (25.96%) versus cold water systems (16.98%) and swab samples (13.51%). A Relative Risk (R.R.) > 1 (p < 0.0001) was calculated for hot water temperature <55 degrees C (R.R.: 4.43), chlorine concentrations <0.2 mg/L (R.R.: 2.69), star ratings <4 (R.R.: 1.73) and absence of Water Safety Plan implementation (R.R.: 1.57).