Beyond Microbiological Analysis: The Essential Role of Risk Assessment in a Travel-Associated Legionnaires’ Disease Outbreak Investigations

Between April and May 2025, an outbreak of travel-associated Legionnaires’ disease (TALD) occurred, involving six cases at a hotel in Crete, Greece. Including two cases reported in 2023 and two additional cases from 2016 to 2017, 10 cases were associated with this accommodation site. All TALD cases were reported by the European Legionnaires’ Disease Surveillance Network (ELDSNet). In accordance with the surveillance and investigation protocols of the European Centre for Disease Prevention and Control (ECDC), local public health authorities immediately upon notification of the cases conducted on-site inspections at the hotel via the collection of water samples and conducting risk assessments, while simultaneously recording the required epidemiological, environmental, and physicochemical data. A total of 181 statistically analyzed water samples showed positive rates for Legionella spp. 13.81% (95% CI: 9.14–19.71) (≥50 CFU/L) and 7.73% (95% CI: 4.29–12.64) (≥1000 CFU/L). Risk assessments identified 18 stagnation points, systemic maintenance deficiencies, and high cumulative structural (30/52) and water (36/71) system risk scores. Low microbiological positivity of water samples does not necessarily equate to low risk, thus necessitating continuous risk assessment, implementation of Water Safety Plans, and integrated monitoring by accommodation facilities to prevent Legionnaires’ disease cases.