[1] A toilet plume[2] is the cloud like dispersal of potentially infectious microscopic sewage particles & water vapor as a result of flushing a toilet. Day to day use of a toilet by healthy individuals is considered to be of a lower health risk. However this dynamic completely changes if an individual is fighting an illness and currently shedding out large quantities of an infectious virulent pathogen (virus or bacteria) in their urine, feces or vomitus. There is evidence that specific pathogens such as norovirus or SARS coronavirus could potentially be spread by toilet aerosols, but no direct experimental studies had refuted actual disease transmission from toilet aerosols. It has been hypothesized that dispersal of pathogens may be reduced by closing the toilet lid before flushing, and by using toilets with lower flush energy. 2024 Science[3] empirically built on to this theory, by illustrating that the viruses that toilet plume contains still spreads out the gaps in the seat onto the walls and concentrating on the surrounding floors.
There is evidence that toilet aerosols generated by flushing can be a vector for diseases that involve acute gastroenteritis with the shedding of large numbers of pathogens through feces and vomit.[4] For example, some epidemiological studies demonstrate transmission of norovirus in passenger airplanes[5] and ships,[6] and SARS coronavirus through a contaminated building sewage system,[7] from flushing contaminated toilets, aerosolizing pathogens rather than other routes.[8] The feces and vomit of infected people can contain high concentrations of diseases many of which are known to survive on surfaces for days, weeks or even months. Toilets are scientifically proven to continue to produce contaminated toilet plumes over multiple successive flushes as indicated in the above video. Some other pathogens speculatively identified as being of potential concern for these reasons include gram-positive MRSA, Mycobacterium tuberculosis, and the pandemic H1N1/09 virus commonly known as "swine flu".
There is 70 plus years of experimental evidence on disease transmission by toilet aerosols. Toilet aerosols are known to contain Norovirus, SARS Coronavirus, Samonella and many other Diseases but not been directly measured . The combination of cleaning and disinfecting surfaces is usually effective at removing contamination, although some pathogens such as norovirus[9] and Salmonella have an apparent resistance to these techniques.
Aerosol droplets produced by flushing the toilet can mix with the air of the room,[10] larger droplets will settle on surfaces or objects creating fomites (infectious pools) before they can dry, like on a counter top or toothbrush; [11] and can contaminate surfaces such as the toilet seat and handle for hours, which can then be contacted by hands of the next user of that toilet. Smaller aerosol particles can become droplet nuclei as a result of evaporation of the water in the droplet; these have negligible settling velocity and are carried by natural air currents. Disease transmission through droplet nuclei is a concern for many pathogens, because they are excreted in feces or vomit. The critical size dividing these dispersal modes depends on the evaporation rate and vertical distance between the toilet and the surface in question.
Experiments to test bioaerosol production usually involve seeding a toilet with bacteria or virus particles, or fluorescent microparticles, and then testing for their presence on nearby surfaces and in the air, after varying amounts of time. The amount of bioaerosol varies with the type of flush toilet. Older wash-down toilet designs produce more bioaerosol than modern siphoning toilets. Among modern toilets, bioaerosol production increases as qualitative flush energy increases, from low-flush gravity-flow toilets common in residences, to pressure-assisted toilets, to vigorous flushometer toilets often found in public restrooms.
Lowering the toilet lid helps prevent dispersion of large droplets, however January 2024 Science authored by Gerba proved that viruses still escape in the Toilet Plume with the lid down. The study recommended discouraging the use of lidless toilets, and thus contradicts the US Uniform Plumbing Code specifications for public toilets.[12]
Experiments on the bioaerosol content of toilet plumes were first performed in the 1950s. A 1975 study by Charles P. Gerba popularized the concept of disease transmission through toilet plumes.[13] The term "toilet plume" was in use before 1999.[14]