Health & Wellbeing

Toilet flush tests reveal just how nasty it is to leave the lid up

Toilet flush tests reveal just how nasty it is to leave the lid up
An automatic toilet flushing device can reduce bacterial spread
An automatic toilet flushing device can reduce bacterial spread
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An automatic toilet flushing device can reduce bacterial spread
An automatic toilet flushing device can reduce bacterial spread
Locations of agar plates for collecting bacteria after flushing
Locations of agar plates for collecting bacteria after flushing

When it comes to toilet etiquette, do you put the lid down before you flush or leave it up? If you said leave it up, the results of a new study by researchers at the Asan Medical Center in South Korea might have you questioning your practices.

Scientists have known for a while that flushing a toilet can spread small particles of water, urine, feces, and pathogens. To see just what a flush was capable of, in 2022, University of Colorado Boulder researchers used lasers to measure the normally invisible aerosol plume created by a commercial toilet without a lid. They found that flushing produced a plume that travelled faster than 2 m/second (6.6 ft/s) and reached a height of 1.5 m/4.9 ft within eight seconds. They captured a video of the icky process.

Shining a light on what comes up when you flush

With hospital patients in mind and determined to keep whatever bugs are in the bowl in there and nowhere else, Asan Medical Center researchers developed an automated toilet flushing device that only works when the lid is closed.

“Human feces can contain a number of disease-causing bacteria, including E. coli, Staphylococcus, and Campylobacter,” said Jihye Park, the study’s lead author. “Any potential means of infection control must be applied to keep patients, especially the most vulnerable, as safe and healthy as possible.”

To analyze the spread of bugs caused by toilet flushing, they fitted their device to four hospital toilets used by patients. Four toilets without the device acted as a control. Eight agar plates used to culture microorganisms were placed strategically on top, in front, to the sides, and behind the bowl.

Each toilet was flushed once when the toilets were clean. Airborne particles were allowed 90 minutes to settle on the surface of the agar plates. The plates were incubated for two days, and then the researchers examined what bacterial colonies had grown. On average, across all locations, less than half as many – six versus 14 – bacterial colonies were found on the surfaces around the toilets fitted with automatic flushing devices compared to those without.

Locations of agar plates for collecting bacteria after flushing
Locations of agar plates for collecting bacteria after flushing

“Our study underscores the importance of closing the lid before flushing and fitting automatic flushing devices to reduce the contamination of the bathroom surfaces,” Park said. “We are now going to install automatic flushing devices in all hospital bathrooms along with automatic UV disinfection to reduce the spread of infection.”

This research only considered bacteria. A study published in February 2024 in the American Journal of Infection Control found that putting the lid up or down prior to flushing household or public toilets of US design had no significant effect on viral contamination of restroom surfaces. This is likely because viruses are smaller in size than bacteria. The study found that the most effective method of reducing cross-contamination associated with toilet flushing included adding a disinfectant to the bowl before flushing, using disinfectants or detergents in the toilet tank, and disinfecting all restroom surfaces.

The current study’s findings will be presented later this month at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID 2024) in Barcelona, Spain. There’s no published paper at this stage.

Source: Asan Medical Center via Scimex

Jose Gros-Aymerich
Bacteria aerosols, and of other common toxic elements are quite frequent.
I can't understand why in some places as France and Germany, they have 'guardians' at the toilette's entrance, exposed to urine odors, and to breathe aerosols of harmful things.
It seems they don't even consider a Ventilation system having Air from the dejection zone sent away, and filtered
Brian M
Perhaps some sort of vacuum/negative pressure 'flush' system?
Or just flush and run!
Back to the outhouses. No flushing, no bacteria?
Valid concerns have also been raised about Dyson hand driers which stir up the air in the bathroom along with the vapor from flushed toilets.
What about airline toilets which primarily suck rather than flush?
Petri dishes are not people. Until experiments are done with larger sample sizes and measure rates of disease transmission to actual people (who generally have immune systems) and not Petri dishes (that don’t), I view studies like these as circumspect, at best.
Aside from that, lowering and raising the seat requires touching it with your hands, hands which can end up transferring germs to the mouth, nose, or eyes. Closing the lid with every flush would result in a fairly high concentration of surface germs on that seat cover unless it was wiped down after every use. In other words, a properly conducted study could easily show that this nifty device increases disease transmission rather than decreases it.
Bacteria are important. Very important. That's why Human babies evolved to stick goddamned everything in their mouths. Just because marketing machines label things "germs" and frighten you into disinfecting everything, doesn't mean that's not doing you more harm than good!
And that's not even *starting* on the importance and benefits of your gut micro-biome ( )!! Stool-transplants exist for a *reason* !
OK, now show a flush with the lid down and see how much will escape out the sides anyway.
Have to agree with the comment left by Zort. My toilet seat leaves a 1/2" gap above the bowl,which hardly slows down the bacterial aerosol surging out from the toilet when flushed.