Evaluating the risk of Clostridioides difficile infection from toilet flushing: A quantitative microbial risk assessment and implications for infection control

Background

Despite stringent infection control measures, Clostridioides difficile infection (CDI) remains a challenge in healthcare settings, partly due to overlooked transmission vectors such as toilet plume bioaerosols.

Aim

To systematically quantify the risks associated with CDI transmission via toilet flushing and provide critical insights to inform CDI preventive strategies.

Methods

Impaction sampling was used to quantify airborne C. difficile post-flush and high-contact surfaces were swabbed to assess contamination levels, in a controlled toilet environment. A quantitative microbial risk assessment (QMRA) approach was then used to estimate the risk to subsequent users from contamination by a previously colonized individual.

Findings

A single flush can release C. difficile into the air, with bioaerosol concentrations up to 29.50 ± 10.52 cfu/m3 and deposit about 8–11 cfu on immediate surfaces. Despite a 4.4 log reduction in bacterial concentration within the toilet bowl post-flush, bacteria persist on its inner walls. Relative humidity increases by approximately 31.28% within the first 10 min post-flush, potentially enhancing the viability and transmission of aerosolized C. difficile. The flush button contact and inhalation-followed-by-ingestion in frequent-use hospital settings present the highest risks and exceed US EPA and WHO acceptable infection risk thresholds.

Conclusion

The findings of this study necessitate a review of current toilet designs, public health policies and facility management practices to mitigate the overlooked risks of CDI transmission through toilet plume bioaerosols in healthcare settings. Additionally, this study lays a foundation for developing evidence-based interventions aimed at achieving substantial behavioural and infrastructural changes in infection control practices.