Background and Objectives:
Thermal waters are used for therapeutic or recreational purposes as baths, inhalation, irrigation and mud therapy. Their peculiar properties, i.e. temperature, pH and concentration of salts, can create habitats suitable for survival and multiplication of opportunistic pathogens such as Legionella spp. To date, there has been no systematic synthesis of literature on Legionella spp. contamination or legionellosis events related to thermal water. This study aims to evaluate the Legionella spp. presence in thermal waters and cases or outbreaks of legionellosis associated with exposure to these waters.

Methods:
PubMed/EMBASE/Scopus/Web of Science/CINAHL were searched for primary studies on Legionella spp contamination in thermal water and on associated cases/outbreaks of legionellosis. Studies were searched up to 12 December 2022. Two PubMed search strategies have been performed: - (legionella OR Legionellaceae), first part for Legionella spp. contamination; - (legionella OR legionellosis OR “Pontiac fever” OR “Legionnaires’ disease”) AND (case* OR cluster* OR outbreak* OR infection* OR investigation OR surveillance), first part for legionellosis cases or outbreaks; - AND (“recreational water” OR spa OR pool OR “hot tub” OR whirlpool OR bath OR “turkish bath” OR Jacuzzi OR “natural spa” OR “hot spring” OR “thermal spring” OR “warm spring” OR spring OR thermal OR mineral waters[mesh] OR hot springs[mesh]), second part for both searches. These search strategies have been adapted for each included database.

Results:
A total of 495 articles for Legionella spp contamination in thermal waters and 394 articles for legionellosis cases/outbreaks associated with these waters were retrieved from PubMed. The search in the other databases is still being carried out.

Conclusion:
Our results will provide a synthesis of the current evidence on Legionella presence and infections associated with thermal waters, useful to evaluate infection risk and possible treatments to control contamination of these resources preserving their characteristics and healing properties.