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

## TL;DR

An outbreak of Legionnaires’ disease at a Greek hotel highlights the importance of risk assessment alongside microbiological testing to prevent future cases.

## Contribution

The study emphasizes the necessity of continuous risk assessment and Water Safety Plans in preventing Legionnaires’ disease.

## Key findings

- Water samples showed 12.71% positivity for L. pneumophila at ≥50 CFU/L and 6.08% at ≥1000 CFU/L.
- Risk assessments identified 18 stagnation points and significant maintenance and structural deficiencies.
- Low microbiological positivity does not indicate low risk, underscoring the need for integrated monitoring.

## Abstract

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, ten cases were associated with this accommodation site. All TALD cases were reported by the European Legionnaires’ Disease Surveillance Network (ELDSNet). In compliance with the European Centre for Disease Prevention and Control (ECDC) surveillance and investigation protocols for hotels associated with the patient’s stay, local public health authorities conducted on-site inspections at the hotel by collecting water samples and performing risk assessments, while simultaneously recording the required epidemiological, environmental, and physicochemical data. A total of 181 statistically analyzed water samples showed positive rates for L. pneumophila of 12.71% (95% CI: 7.86–17.56) for (≥50 CFU/L) and 6.08% (95% CI: 2.60–9.56) for (≥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 (WSPs), and integrated monitoring by accommodation facilities to prevent LD cases.