Frank Bures: Potty plumes and COVID-19 infections

Frank Bures: Potty plumes and COVID-19 infections

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A paper from Yangzhou University, China, was published June 16 in the journal Physics of Fluids (no intended pun) about the water vapor plume that flies out of the toilet after flushing.

It has raised kind of a stink regarding possible infection from inhaling airborne COVID-19 viral particles from someone with the disease.

There is actually quite a history of the idea that the potty plume can send potentially infectious droplets into the air and onto surrounding surfaces for other infectious organisms that may be contained in flushed feces.

The likelihood of you either breathing in enough viruses as droplets or touching them in sufficient density to transmit infection via oral or nasal exposure is quite low, according to the CDC and World Health Organization.

The major mode of infection is thought to be inhaling respiratory airborne droplets. The current paper used computer models to generate the data. It showed the turbulence from the flushed water could send a plume in a vortex 3 feet high. The aerosol, a suspension of viral particles in the mist, can last a minute before dissipating, and can float around the room to floors and other surfaces.

Some questions swirling around this hypothesis are whether the droplets carry fragments of non-viable and non-infectious virus or viruses live and kicking.

Several genetic studies have previously found the COVID-19 virus in stool samples. At least one study showed those found can be infectious. And a May 18 report from the CDC found viable and infectious virus in fecal excretions in a small group of patients.

To date, there is only indirect evidence that potty plume can be a vector for diseases. There is yet no experimental evidence on direct transmission via this route.

An association between inhalable bioaerosols produced from disturbed sewage and the transmission of infections has been proposed for more than 100 years.

The first bioaerosol production from toilet flushing was reported in the 1950s. Several toilet types have been “seeded” with bacteria. Culture plates were set around at varying distances and times from the bowl, and air samples collected. In addition to what was collected on the floor, bacteria were still being captured from the air eight minutes after the flush.

Many other seeding and flushing studies were also analyzed in a review 2013 paper in the American Journal of Infection Control entitled “Lifting the lid on toilet plume aerosols: A literature review with suggestions for future research.”

Various organisms were used, from E. coli to salmonella to serratia to clostridium. The results had the same theme of persistent bacteria from subsequent flushes, as well as spread of microbes around the immediate area.

The current study did not perform any real biological evaluations. The authors are physicists, not biologists. The recommendation they came to was to close the toilet lid before triggering the flushing process.

A Washington Post article republished in the June 17 Minneapolis Star Tribune was titled “Latest advice: Close toilet lid, then flush.”

Two days later, a letter to the editor very pragmatically noted that public toilets do not have lids. So, what advice do the experts have here? Of course, the answer is not much. The Chinese study’s lead author said manufacturers should design a new toilet, in which the lid is automatically put down before flushing. An invention waiting to happen.

The experiments necessary to prove cause and effect/infection are not likely to be performed. Finding volunteers, even broke medical students, for investigating the elements of the dark, moist maelstrom expelled from toilet flushes are unlikely.

The question of how hazardous the plume particles are remains up in the air. Practical measures here, especially in public restrooms, are always to wash your hands well. The Chinese suggest wearing a mask even in the “water closet” (a bit British).

An interesting aside, which we wrote on some years back, is whether you tend to leave the toilet lid up or put it down after use, not so much during flushing.

The geographical difference was Easterners, lid down, Midwesterners, up. Now, maybe we’ll all close the lid. Gone will be the potty training experience of watching with your cherub, his or her contribution to recycling swirl down the drain.


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