Serial Surveillance of Viable Bacterial Contamination in a German Hotel Across Pre-COVID and Pandemic Recovery Periods: Persistent Hotspots and Functional-Area Heterogeneity

Hotels contain diverse functional environments, yet longitudinal evidence on viable bacterial contamination and its response to COVID-associated hygiene changes remains limited. This retrospective serial cross-sectional study analyzed 544 environmental samples from five audits of a German hotel conducted in 2016, 2018, 2019, 2022, and 2023. Pre-pandemic audits (2016, 2018–2019) were compared with 2022–2023 audits across four functional environments: guest rooms, child-oriented areas, wellness/water facilities, and food-service operations. Outcomes included culture positivity, contamination severity, polymicrobial and priority-microorganism detection, persistent hotspots, and organism distributions. Modified Poisson models adjusted for functional environment and used cluster-robust inference. All statistical analyses were performed in R (version 4.5.1). High contamination declined from 54.2% pre-COVID to 19.3% in 2022–2023 (aPR, 0.36; 95% CI, 0.25–0.54; p < 0.001), an adjusted reduction of 34.1 percentage points (95% CI, 21.5–46.6). Culture positivity remained unchanged (63.4% vs. 60.1%; aPR, 0.96; 95% CI, 0.83–1.12; p = 0.634), whereas polymicrobial contamination decreased (aPR, 0.61; 95% CI, 0.39–0.96; p = 0.032; adjusted reduction, 8.3 percentage points; 95% CI, 1.0–15.7). Priority-microorganism detection was unchanged (aPR, 1.06; 95% CI, 0.67–1.67; p = 0.804), despite a shift toward S. aureus and P. aeruginosa. Culture positivity remained approximately 90% in child-oriented and food-service areas. Eight of 15 recurring surface categories remained persistent hotspots, including wet-room floors, frequently touched controls, paddling-pool features, and food-service machinery. The Bacillus cereus group decreased from 12.6% to 2.5%, whereas Staphylococcus aureus and Pseudomonas aeruginosa were each detected in 0% versus 5.8% of samples (q < 0.001). Audits in 2022–2023 showed lower contamination intensity without corresponding reductions in overall culture positivity or priority-microorganism prevalence. Complementary burden-, complexity-, and organism-based indicators are needed for environmental-hygiene evaluation.