A Hybrid Occupational Risk Assessment of Legionella pneumophila in Hotel Water Systems Associated with TALD Cases

Travel-associated Legionnaires' disease (TALD) investigations in hotels have generated extensive environmental monitoring data. However, the occupational implications for workers who operate, maintain, clean, or inspect the same systems are rarely assessed. We developed a hybrid framework integrating a semi-quantitative environmental hazard model with deterministic Quantitative Microbial Risk Assessment (QMRA). In the first model, culture concentration bands were combined with physicochemical deviation indicators (temperature, free residual chlorine, and pH) to derive point-level hazard (Hi) and zone-level hazard (H¯z). In the second model, a job-based presence matrix was combined with zone-specific serogroup-based severity using a simplified World Health Organization (WHO)-style 3 × 3 likelihood-severity approach. Legionella pneumophila (≥50 CFU/L) was detected in 29.94% of water samples and was significantly associated with low chlorine (<0.2 mg/L; RR 2.90) and hot water temperature < 55 °C (RR 3.07). To support comparative occupational exposure stratification, QMRA was applied to estimate the daily inhaled dose (d) for 15 worker groups, indicating variability in modeled biological exposure across occupational categories. Within this framework, modeled occupational exposure potential was shaped by the combined influence of pathogen concentration and assumed exposure duration. Under the hazard model, the highest zone-level hazard estimate was observed in kitchens and food and beverage (F&B) areas (H¯z = 2.607), followed by machinery rooms (H¯z = 2.022) and guest rooms (H¯z = 1.874). These findings support the integration of worker protection into water safety management, particularly in areas and groups overlooked in routine investigations.