Surface microbiological surveillance in a crowded emergency department: interplay of environmental pressure, construction, and disinfection efficacy

Environmental surface contamination in Emergency Departments (EDs) is a recognized contributor to pathogen transmission. However, its relationship with organizational and environmental stressors remains insufficiently characterized. Between January and November 2025, monthly microbiological surface surveillance was conducted in a tertiary ED with approximately 70,000 annual visits. Standardized sampling using contact plates (25 cm 2 ) targeted predefined sites, including high-touch surfaces, equipment, and walls. Indicator organisms included Staphylococcus aureus, Bacillus spp., and Enterobacteriaceae. Environmental factors, including ED occupancy and construction activities, were documented. Cleaning protocols remained unchanged throughout the study. Bacillus spp. contamination was predominantly observed during construction phases, consistent with environmental dust dispersion. Elevated S. aureus contamination coincided with periods of severe overcrowding (up to 98% occupancy). During a control period with low activity and no construction, no indicator organisms were detected on sampled surfaces. Enterobacteriaceae were only sporadically identified. Surface contamination patterns were strongly associated with environmental and organizational stressors rather than disinfection failure. Microbiological surveillance may serve as an operational indicator of system strain in emergency care settings.