Environmental and Health Care Personnel Sampling and Unobserved Clostridium difficile Transmission in ICU.

Clostridioides difficile is among the most prevalent health care-associated pathogens worldwide. Controlling it remains a critical challenge, due in part to spore viability on surfaces. To quantify transmission of C difficile within health care facilities and evaluate the roles of environmental surfaces and health care personnel (HCP) hands in C difficile movement. In 2018, a 13-week longitudinal, observational study was conducted in 2 intensive care units (ICUs) in Utah with daily culture-based sampling of patient body sites, room environmental surfaces, HCP hands, and shared environmental surfaces. Both toxigenic and nontoxigenic C difficile strains were selected for whole genome sequencing and included in the analysis. Data were analyzed from September 2021 to September 2024. The primary outcome was the identification of transmission clusters based on genomic relatedness between isolates from patients, environmental surfaces, and HCP hands. Clusters were defined as isolates with 2 or fewer single nucleotide variants between them. Of the 278 unique ICU admissions, 177 patients consented to body site sampling and were sampled. Along with these, environment surfaces and HCP hands were sampled daily for all occupied rooms, leading to 7000 total samples. Sampling patients, their environment, and HCP hands revealed that nearly 8% of all patients had C difficile linked to other admissions and 57% of transmission clusters bridged nonoverlapping patient-stays. Including environmental surfaces and HCP hands, a 3.6-fold higher C difficile movement was identified than with patient sampling alone, highlighting environmental surfaces as reservoirs. These results challenge the idea that nosocomial transmission is not a primary source of acquisition and underscore the importance of hand hygiene and environmental decontamination. This study reinforces the need to include environmental surfaces and HCP hands in future work characterizing the burden of nosocomial transmission. Understanding the transmission pathways of C difficile within health care facilities, particularly the roles of environmental surfaces and HCP hands, is critical to improving infection control measures.