| Abstract |
Introduction: Legionnaires' disease has been linked to travelling and staying in hotels. It can cause severe pneumonia, which can be often underdiagnosed. Causative agent is Legionella, with L. pneumophila accounting for about 90% of Legionellosis cases. In Europe, 1.657 cases of legionnaires’ disease linked with travelling (TALD cases) were reported in 2019. In Greece, as in the rest of the Mediterranean countries, temperatures are more favourable for the growth, and multiplication of the bacterium in water distribution systems.
The aim of this doctoral thesis was to investigate the colonization levels of hotel water storage and distribution systems by Legionella spp in Crete and the risk factors involved. In addition, we compared the characteristics of hotels with TALD cases and a random sample of facilities. Lastly, we performed descriptive analysis of the TALD cases that had travelled to Crete between 2000-2018 and explored trends in reporting numbers.
Methods: Sample collection and risk assessments of the study hotels, were carried out by the local public health authorities according to the European technical guidelines. Laboratory analysis of the samples were performed according to the international ISO 11731 (1998), and ISO 11731-2 protocols. Further colony characterisation was performed using the MALDI-TOF spectrometer and molecular epidemiology tools (sequencing and phylogenetic analysis according to the international SBT scheme for L. pneumophila strains or the mip and 16S rRNA genes for the rest of the strains). Statistical processing of the results was performed with the software: MS Excel, STATA v11, RStudio v1.1.447, MEGA4 and ClustalW2.
Results: From 2000 to 2018, 180 TALD cases were reported in Crete. The distribution of cases followed the known seasonality of TALD cases, from April to November, while there was an increasing trend in the number of cases during the study period. During the study comparing hotels with TALD cases and a random sample of hotels (total of 33 hotels), both groups had similar colonization rates, but the first group had higher colonization rates of L. pneumophila serogroup 1, which is responsible for most cases internationally. During the main study, we collected 3311 water samples from 132 hotels. The Legionella colonization was 21% of the water samples, coming from 83 (63%) hotels. The most common species isolated were L. pneumophila serotype 1, 3 and 6, as well as non pneumophila species in a smaller number of samples. Deviation of the hot water temperature from the legislation limits seemed to be the most important factor for the colonization by Legionella. Furthermore, the non-satisfactory implementation of water safety plans (WSP), the low concentration of residual chlorine in the water systems and the size of the hotel (<80 beds) also increase the risk of colonization. According to the results from the molecular surveillance, the L. pneumophila ST37 was the predominant circulating strain in the island, along with some non pneumophila strains (e.g. L taurinensis, L. anisa).
Conclusions: The efficient management and prevention of TALD cases in the island of Crete, is of high importance, as the local community depends heavily on tourism economy. At hotel unit level, the proper installation and implementation of a WSP tool, with constant control of water quality points, can significantly reduce the risk of colonization by Legionella bacteria. At regional level, the development of a central active surveillance system can contribute to the effective control of Legionella, through systematic inspections and testing of water samples from the environment of all hotel units on the island, regardless of their possible connection with a legionellosis case. Such a system would also offer additional information on trends, detection of new strains, measuring the effectiveness of disinfection and providing timely information for action.
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