Do Your Part, Close The Lid
The first warnings about the hazards of vigorous flushing
began to appear six months into the COVID-19 coronavirus pandemic,
in the summer of 2020.
Several studies were demonstrating that "toilet plumes"
launched by turbulent flushes could spread the pandemic.
We know two things.
First, infected people shed viral particles in their feces.
Second, turbulent water and air flow launch a geyser of fecal mist,
an aerosol of poop-borne pathogens.
And so, it's important to close the lid before flushing!
It's especially important for public toilets.
Or at least it would be important,
if public toilets have lids.
Unfortunately, they seldom do.
But if you can, close the lid!
Toilet at Iggy's bar on the Lower East Side in New York City.
As usual, a seat but no lid.
Shedding Viral Particles
On May 18, 2020, researchers in Guangzhou, China, published a
later appear in the August issue of Emerging Infectious Diseases.
They had detected viral RNA in feces and urine of several patients.
It started in January, when a man who had recently traveled to Wuhan
was admitted to the hospital.
Quantitative reverse transcription PCR detected SARS-CoV-2 RNA in swabs
from his nose and throat.
They collected fecal specimens, which also contained viral RNA.
What's more, transmission electron microscopy showed spherical
viral particles with the distinctive protein spikes.
So, not just molecular scraps, but infectious virus particles.
A virus isn't alive, as biology defines that term.
It doesn't consume any nutrients, or excrete any waste.
It can't reproduce itself, the cells of the infected organism
are hijacked to replicate it.
Many strains of virus, including the SARS-CoV-2 coronavirus,
are encased in a lipid or fatty shell.
You can't kill what isn't alive, but detergent molecules in soap
can break down the lipid coat, leading to the virus being torn apart.
Wash your hands!
first U.S. case
had viral genetic material in his stool.
At the time it was still called 2019-nCoV,
"the novel coronavirus that appeared in 2019".
My toilet in West Lafayette, Indiana.
I should close the lid before flushing!
We've Seen This Before
We referred to the 2002-2004 pandemic simply as SARS,
Severe Acute Respiratory Syndrome.
It also arose in animals in East Asia before crossing to humans.
There were only 8,422 known cases.
The low case count was good, as SARS had a Case Fatality Rate of 11%.
MERS or Middle East Respiratory Syndrome appeared in 2012.
It first appeared in bats, then moved to camels,
the source of most human cases.
35% of those diagnosed with this disease die from it.
Both SARS and MERS are caused by coronaviruses,
SARS-CoV-1 and MERS-CoV, respectively.
Both of them have spread by fecal-oral or fecal-respiratory routes.
And, SARS-CoV-2 seems equally capable of spreading through feces.
Potential for aerosolization of Clostridium difficile
after flushing toilets:
the role of toilet lids in reducing environmental contamination risk
in The Journal of Hospital Infection dating back to 2011
described a study about airborne transmission of Clostridium difficile
caused by flushing toilets without lids.
They detected C. difficile spores
up to 25 centimeters above the toilet seat.
C. difficile infection causes watery diarrhea leading to dehydration,
severe abdominal pain,
loss of appetite, fever, and nausea.
Worse cases can lead to life-threatening colitis or inflammation of the colon.
People are most often infected in medical care settings such as hospitals and
Within a month of the Emerging Infectious Diseases. paper,
appeared in Physics of Fluids.
Three physicists from Southeast University in Nanjing,
Suzhou University of Science and Technology,
and Yangzhou University observed that both our design and use of toilets
contributes to spreading disease.
They refer to toilets as examples of
"the daily but dangerous necessities of life."
Some toilets have a single inlet for flushing water.
However, an annular flow design is more common.
Water flows from a gravity-feed tank or from a pressurized supply to a
ring of outlets around the lower side of the rim.
The fluid dynamicists report that airflow vortices will appear no matter
how the toilet is flushed, and the centrifugal forces generated by those
vortices lead to high airflow speeds.
They estimate that an average of 2,700 particles are propelled
up and out of the toilet bowl during a one-shot single-inlet flush.
The annular flushing design causes stronger turbulence,
and lofts more particles out of the bowl.
Nearly 60% of the total collection of aerosol particles rise above the
rim of the bowl, with an initial upward velocity as high as
five meters per second.
Even 35 to 70 seconds after the flush, diffused particles are still climbing
at a much slower velocity.
The toilet plume reaches a meter or more above the floor,
eventually spreading to surfaces throughout the room.
Toilet at Harry's bar in West Lafayette, Indiana.
No lid, not even a seat.
Public toilets like this, with an annular water inlet and high pressure
flushing, seem to have been designed to spread infectious aerosols.
Their recommendations are unsurprising, and easy to carry out
if the toilet has a lid:
Aerosol generation in public restrooms
Clean the lid before using the toilet.
Floating virus particles may have settled on its bottom surface.
Lower the lid before flushing.
Wash your hands thoroughly after using the toilet,
because virus particles may have settled on the flush control and door handle.
in Physics of Fluids found that a flushing toilet can create a plume
at least 1.52 meters high
made up of droplets in the 0.3–3 μm size range.
Multiple flushes built up the ambient aerosol level,
meaning that a busy public toilet would be more dangerous.
Commercial toilets emit energetic and rapidly spreading aerosol plumes
Then a December 2022
reported on how bad common public toilets are in this regard.
They also found that aerosols reached a height of 1.5 meters.
The paper includes a video of a laser-illuminated toilet plume.
Squat toilet in Guangxi, China, near the
Squat toilets are looking better and better.
They're down in the floor, while a raised throne commode gives the
fecal plume a 30 cm head start on reaching the level of your
mouth and nose.
The flow from a hose like the above one could provide a smooth flush.
You want flowing water to wash down the waste but without the turbulence
that lofts an aerosol of pathogens into the room.
Of course Japan has toilet lids that automatically open when you approach,
and close as you flush.
Along with many other toiletological wonders.
"Far-UVC inactivates coronaviruses"
The next must-have home accessory may be a toilet lid
that automatically closes before the flush begins.
With, of course, built-in far-UVC illumination to deactivate the virus.
"Far-UVC light (222nm) efficiently and safely
inactivates airborne human coronaviruses", by Buonanno, Welch, Shuryak,
and Brenner, Nature: Scientific Reports,
SARS Spread Within a Building's Sewage System
In 2003, 329 residents of Amoy Gardens, a private housing estate in Hong Kong,
were infected with SARS.
Investigation and analysis showed that the building's sewage pipelines
had aerosolized contaminated feces, which emerged from other apartments'
Looking north up Nathan Road in the Tsim Sha Tsui district
at the tip of the Kowloon Peninsula in Hong Kong.
Dried-out floor drains were blamed for transmission between apartments.
The water normally standing in the S-shaped traps evaporated to the point
that they no longer formed an air lock or air seal.
You can expect a typical trap to dry out and break seal within 30 days.
So, more lessons were learned:
Pour some water into your floor drains at least once a month.
Keep the traps filled with water and keep the pathogens out of your home.
For the same reason, use your shower or bathtub at least once a month.
Chungking Mansions on Nathan Road in the Tsim Sha Tsui district
at the tip of the Kowloon Peninsula in Hong Kong.
In September 2020, a new
paper in the Annals of Internal Medicine
described a case of three infected families
in a high-rise building in Guangzhou, China.
One of the families had traveled to Wuhan, the epicenter of the 2019 outbreak.
The other two families had not traveled,
and began exhibiting symptoms after the first one.
Apparently the first family infected the other two.
The three families lived in three vertically aligned apartments
in Block X, one of thirty high-rise housing blocks in a
6-year-old private housing estate.
Shared drainage pipes and vents run vertically through the building.
These allowed aerosolized pathogens to move between apartments.
paper in Environment International
listed the various forms of aerosol and droplet spread.
It then described the discovery of SARS-CoV-2 on surfaces in the
bathroom of a long-vacant apartment which was directly above
the bathroom of an apartment of five people infected with COVID-19.
That was also in Guangzhou, probably the same cluster of cases.
Guest room in the Chungking Mansions in the Tsim Sha Tsui district.
I arrived at Hong Kong late in the evening,
landing at the new airport and taking a bus into the city.
I showed up at the Chungking Mansions to see what the touts would offer.
It's a massive multi-story apartment building,
with many apartments converted to guest houses.
It was late, but people were still offering guest rooms.
I ended up in the spare bedroom of the manager of a guest house.
It wasn't large, just barely big enough to hold a bed that was
just barely big enough for me, not completely stretched out.
It connected to a bathroom that was, by Hong Kong guesthouse standards,
It had a toilet, sink, and shower, as three separate fixtures.
In another guesthouse later in the trip, my bathroom compartment was
really just a shower, which had a toilet and sink within the shower space.
Guest room with spacious attached bathroom
in the Chungking Mansions in the Tsim Sha Tsui district.
The street level and the new two floors above that
are filled with shops and restaurants.
The many floors above that are filled with apartments.
Some of them have been converted to guesthouses.
Others have been converted to curry shops.
Stairwell in the Chungking Mansions in the Tsim Sha Tsui district.
There are shared public toilets down in the bottom three levels,
at the street and just above that.
Shared public toilets in the Chungking Mansions in the Tsim Sha Tsui district.
A pandemic is an especially bad time to use a
To read more:
"Evidence for Gastrointestinal Infection of SARS-CoV-2"
Ye Liu,6 Xiaofeng Li,7 and Hong Shan,
in Gastroenterology 2020;158:1831–1833.
"Air, Surface Environmental, and Personal Protective Equipment Contamination
by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)
From a Symptomatic Patient"
by Sean Wei Xiang Ong, Yian Kim Tan, and Po Ying Chia,
of the National Centre for Infectious Diseases, Singapore,
Journal of the American Medical Association,
accepted for publication February 27, 2020.
"First Case of 2019 Novel Coronavirus in the United States"
by the Washington State 2019-nCoV Case Investigation Team,
New England Journal of Medicine,
March 5, 2020.
By 2021 the wastewater monitoring work was well underway and getting
organized on a global scale.
COVID-19 Wastewater-Based Epidemiology
See especially their
and their interactive
Making Textiles? You'll need Urine, Seaweed, and Shale