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

Travel-associated Legionnaires’ disease (TALD) investigations in hotels generate 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 (Hz). 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. L. 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 <50 °C (RR 3.00). To enhance precision, QMRA was applied to estimate the daily inhaled dose (d) for 15 worker groups, indicating variability in modeled biological exposure across occupational categories. These findings suggest that occupational risk is shaped by the combined effect of pathogen concentration and exposure time. Under the hazard model, the highest zone-level hazard estimate was observed in kitchens and food and beverage (F&B) areas (Hz = 2.607), followed by machinery rooms (Hz= 2.022) and guest rooms (Hz= 1.874). These findings support the integration of worker protection into water safety management, particularly in areas and groups overlooked in routine investigations.