Beyond Flushing

The first Healthy Buildings Network seminar of 2025 brought together two leading experts in the field of environmental microbiology and hygiene to explore a topic that affects every building worldwide, toilet hygiene and pathogen transmission. Prof. Chuck Gerba from the University of Arizona and Dr. Khalid Iljaz from Reckitt Benckiser shared fascinating insights into how pathogens move through our built environments, with a special focus on bathrooms and toilets.

Meet the Speakers

Professor Chuck Gerba

Environmental Virologist, University of Arizona

Prof. Gerba is a renowned environmental virologist with decades of experience studying the transmission of viruses in indoor environments. His pioneering work on surface contamination and bathroom hygiene has reshaped our understanding of pathogen transmission.

Dr. Khalid Iljaz

Microbiology Expert, Reckitt Benckiser

Dr. Iljaz specialises in aerobiology and public health, bringing both academic expertise and industry experience to his research on pathogen control. His work focuses on developing effective interventions to break the chain of infection transmission.

The Dynamic Nature of Pathogen Transmission

A central theme from both speakers was that pathogen transmission is not static but highly dynamic. As Dr. Iljaz emphasised, "It's not either/or, it's dynamic interdependent." Microorganisms move continuously between surfaces and air in what he called a "surface contamination network."

Prof. Gerba demonstrated this dynamic through his research on toilet plumes - the aerosols generated when toilets are flushed. His team used viral tracers similar to norovirus to track contamination patterns:

Their findings challenge common assumptions about bathroom hygiene:

• Myth busted: Closing the toilet lid during flushing doesn't significantly reduce contamination. The pressure forces aerosols out from the sides, contaminating toilet seats and surrounding areas regardless.
• Concerning revelation: Viruses from toilet flushing can move beyond the bathroom through human activity, as Prof. Gerba noted, "What is in the restroom doesn't stay in the restroom."
• Unexpected finding: Cleaning toilets with a brush without disinfectant actually spreads contamination throughout the bathroom.

Dr. Iljaz reinforced these findings by demonstrating that pathogens exist in a continuous cycle between air and surfaces. His research showed that walking across contaminated floors, vacuuming, or even sitting on soft surfaces can resuspend settled viruses back into the air.

Targeted Hygiene: When and What to Clean

One of the most practical insights from the seminar came from Prof. Gerba's studies on optimal cleaning frequency. Counter to intuition, daily cleaning wasn't necessarily best. His research found:

• The bathroom becomes most contaminated on day three after cleaning
• Cleaning twice per week (every 3-4 days) provided the maximum benefit
• This pattern may relate to biofilm development, with day three representing peak vulnerability

"Twice a week it turned out to be was a good idea to clean it if you want to do the maximum benefit of your product," Prof. Gerba explained. This cleaning frequency achieved approximately 99% risk reduction when using appropriate disinfection products.