There is a risk that an infectious aerosol is produced when toilets are flushed. One way of addressing this would be to add a disinfectant to the toilet before flushing. But would this be safe and effective?

Since we seem to have having a bit of a watery theme on Reflections in recent weeks (sinks, sinks, or possibly no sinks), I thought I’d continue that with a delightful lunchtime discussion about flushing the loo. There’s a host of evidence (reviewed here) that flushing the loo creates a plume aerosol that can contain infection agents. It’s easy to see how this could be a risk for transmission. One approach to address this is to add a disinfectant to the loo before flushing.

A US team performed a study where phage were inoculated into the toilet bowl along with a human waste surrogate solution before flushing. They established that flushing the loo results in widespread dissemination of the phage around the surfaces of the toilet and the washroom. Then, they showed that adding disinfectants (sodium hypochlorite, hydrogen peroxide, QAC, and peracetic acid) to the loo resulted in a significant reduction in phage contamination. Unsurprisingly, peracetic acid was best, and hydrogen peroxide (which is more prone to inactivation through contact with organic matter) was worst.

Figure: Impact of adding disinfectant to the toilet bowl with various contact times.

A couple of reflections:

The authors didn’t go on to test the impact of disinfection of the loo on actual deposition around the washroom, although you’d expect the sort of reductions in phage concentration measured to translate into a reduction in contamination.

Are the contact times realistic? You probably won’t add disinfectant and then wait around for a minute before flushing.

Would flushing a toilet bowl full of disinfectant be safe? Or perhaps we’d be out of the frying pan of microbial exposure and into the fire of chemical exposure! Clearly, this would need to be tested before being implemented.

Was their ‘synthetic poo’ up to the task? I am not sure that a vial of tryptone soya broth is a worst case scenario of human waste!

The article is interesting, and perhaps paves the way for research on more regular disinfection of the loo. But, for now, the best way to minimise the potential impact of toilet flushing plumes is to close the toilet lid before flushing!