How Clean Is Clean? New Study Reminds Us to Put a Number on Hospital Surface Microbial Burden

Recently, a study by Legeay, et al. (2026) examined the microbial burden and potential pathogens on hospital surfaces before and after cleaning, evaluated the impact of an educational intervention targeting environmental services (EVS) staff, and assessed the relevance of two cleanliness thresholds (4 CFU/cm2 and 2.5 CFU/cm2) for predicting pathogen presence.

This prospective study was conducted over a five-month period across 10 wards in a 1,600-bed university hospital. Surface contamination was assessed weekly using contact agar plates to sample 15 high-touch surfaces and floors in randomly selected rooms, both before and after routine cleaning. Cleaning performance was concurrently monitored using fluorescent markers. In addition, the researchers say a two-day training program was delivered to half of the EVS staff.

Microbial burden (CFU/cm2), the prevalence of contaminated surfaces, and the presence of clinically relevant pathogens were analyzed. A total of 736 samples were collected. Cleaning significantly reduced the overall microbial burden (mean 1.05 vs. 0.75 CFU/cm2, p < 0.001) and pathogen prevalence (19.0% vs. 13.1%, p = 0.03). Floors were the most frequently contaminated surfaces, whereas high-touch surfaces exhibited lower contamination rates. Pathogen presence was strongly associated with higher bioburden: 53 percent versus 10 percent for surfaces with >4 CFU/cm2 compared with those with ≤ 4 CFU/cm2, and 56.3 percent versus 5.9 percent for surfaces with >2.5 CFU/cm2 compared with those with ≤ 2.5 CFU/cm2 (p < 0.0001 for both). The educational intervention significantly improved cleaning compliance as assessed using fluorescent markers (40.3 percent versus 62.8 percent), though reductions in overall bioburden were not statistically significant.

The researchers found that a substantial proportion of hospital surfaces remained contaminated with pathogens even after routine cleaning. They point to other studies, such as one conducted across four hospitals in England that found half of the sampled surfaces yielded >103 CFU/cm2 (Watson, et al., 2023), and the study by Jinadatha, et al. (2024) that confirmed clinically relevant pathogens are frequently detected on high-touch hospital surfaces. They note that, “Lower microbial thresholds, particularly a threshold of 2.5 CFU/cm2, may be relevant indicators of cleanliness for high-touch surfaces. Targeted training improved cleaning practices and showed a trend toward bioburden reduction, highlighting the importance of structured interventions in HAI prevention strategies.”

This study has several limitations: Sampling was performed one to two hours after cleaning, which may have allowed for recontamination and could have led to an underestimation of cleaning efficacy, the researchers say. They did not collect patient-level microbiological data and therefore could not assess the relationship between patient colonization or infection and environmental contamination. Additionally, although EVS staff members were blinded to marked rooms, they were aware of the audit so it is possible that the Hawthorne effect contributed to improved cleaning efforts.

In all, it’s a study worth considering, as it emphasizes that environmental cleaning and disinfection should be conducted as frequently as budget and staff will allow, and that healthcare leaders must provide the resources necessary to support this critical function.

Until next time, bust those bugs!

References:

Dancer S. J. (2023). Hospital cleaning: past, present, and future. Antimicrob. Resist. Infect. Control.12:80. doi: 10.1186/s13756-023-01275-3

Jinadatha C, Navarathna T, et al. (2024). Understanding the significance of microbiota recovered from health care surfaces. Am. J. Infect. Control52, 220–224. doi: 10.1016/j.ajic.2023.11.006

Legeay C, Lemarié C and Eveillard M. What are the microbial burden and potential pathogens on hospital surfaces before and after cleaning? Front. Microbiol., July 14, 2026. Sec. Antimicrobials, Resistance and Chemotherapy. Vol. 17 – 2026 | https://doi.org/10.3389/fmicb.2026.1835355

Watson F, Wilks S, et al. (2023). Evaluating the environmental microbiota across four National Health Service hospitals within England. J. Hosp. Infect.131, 203–212. doi: 10.1016/j.jhin.2022.11.001