**1. Introduction**

*Legionella* is a Gram-negative bacterium found ubiquitously in aqueous environments, which can multiply quickly in man-made water systems [1]. *Legionella* spp. have a complex life cycle, and exist in the environment as free-living bacteria in microbial consortia of environmental organisms or as intracellular pathogens. *L. pneumophila* has plenty of virulence factors, which it uses effectively to infect aquatic protozoa or human lung alveolar macrophages [2].

*L. pneumophila* is the major causative agen<sup>t</sup> of Legionnaires' disease (LD), a severe pneumonia with a fatality rate of up to 15%, and a flu-like illness called Pontiac fever [3,4]. Humans can

contract the disease during exposure to contaminated water aerosols generated by hot and cold water systems, cooling towers, showering facilities, and spa pools [5]. *Legionella* bacteria is an opportunistic pathogen [2]. The risk factors include old age, underlying diseases, and smoking [6]. Although many *Legionella* spp. are considered potentially pathogenic for humans, *Legionella pneumophila* (Lp) causes the vast majority of LD cases, and of the 16 known Lp serogroups (sg), sg1 accounts for over 80% of LD cases [7,8].

Legionellosis is often associated with staying in hotel accommodations, and LD is recognized as a major form of travel-associated pneumonia (TALD) [9]. Since 2010, TALD cases have accounted for 20% of all reported LD cases in Europe each year. The number of cases reported to the European TALD surveillance scheme continues to rise annually, with a 20% increase observed between 2014 and 2015 [10]. Moreover, *Legionella pneumophila* has significant outbreak potential. Since its first fatal outbreak in a hotel in Philadelphia, United States, in 1976, many clusters and outbreaks linked to hotel settings have been investigated globally [11–14]. Factors shown to contribute to the *Legionella* spp. spread and colonization are the complexity, old age, and poor maintenance of a distribution system, warm water temperature, and the presence of amoebae [1,15–17]. Several recent studies have focused on the prevalence and distribution of *Legionella* in water systems of hotels in non-outbreak situations. These studies revealed variable rates of contamination and species diversity [18–21], but limited data is published on the molecular diversity of *Legionella* spp. in hotel settings [22–24].

In Israel, where international and domestic tourism is an important branch of the national economy, TALD has accounted for 15% of all LD cases between 2006 and 2011 [25]. According to recent national epidemiology surveillance data of the Ministry of Health, the majority of TALD cases in Israel are sporadic or imported from abroad, and no major change in trends was observed during the last decade. While isolates from TALD cases undergo molecular typing, a few of them have been linked to a specific accommodation sites. It is likely that a grea<sup>t</sup> proportion of cases go unnoticed, due to the mild symptoms and underdiagnosis, the long incubation period of *Legionella* spp., and the short-term nature of domestic tourism. Of note is that no comprehensive data are available concerning the abundance of *Legionella* spp. in Israeli hotel water systems. In this study, we investigated, for the first time, the prevalence and characteristics of environmental *Legionella* spp. in the Israeli hotel setting as part of routine inspections.
