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Actual "Sneeze Effect" without backlighting

The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet. (note conclusion and impact underlined below)

(Short version)

Barker J, Jones MV.

Department of Pharmaceutical and Biological Sciences, School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, UK. j.e.barker@aston.ac.uk

Summary

Flushing produces aerosols from the force of the water running down the surfaces of the bowl and from the turbulence caused by mixing with water contained in the bowl. Closing the lid had little effect in reducing the number of bacteria expelled into the air after flushing. Although splashes could be contained by closing the lid, there is a gap between the top of the porcelain rim and seat, and a gap between the seat and lid allowing aerosols to escape.

The possibility that aerosols containing enteric pathogens could cause infection after being swallowed following deposition in the nose or pharynx has been suggested and can be true for norovirus infection.

AIMS: To determine the level of aerosol formation and fallout within a toilet cubicle after flushing a toilet contaminated with indicator organisms at levels required to mimic pathogen shedding during infectious diarrhoea. METHODS AND RESULTS: A semisolid agar carrier containing either Serratia marcesens or MS2 bacteriophage was used to contaminate the sidewalls and bowl water of a domestic toilet to mimic the effects of soiling after an episode of acute diarrhoea. Viable counts were used to compare the numbers of Serratia adhering to the porcelain surfaces and those present in the bowl water before and after flushing the toilet. Air sampling and settle plates were used to determine the presence of bacteria or virus-laden aerosols within the toilet cubicle. After seeding there was a high level of contamination on the porcelain surfaces both under the rim and on the sides of the bowl. After a single flush there was a reduction of 2.0-3.0 log cycles cm(-2) for surface attached organisms. The number of micro-organisms in the bowl water was reduced by 2.0-3.0 log cycles ml(-1) after the first flush and following a second flush, a further reduction of c. 2.0 log cycles ml(-1) was achieved. Micro-organisms in the air were at the highest level immediately after the first flush (mean values, 1370 CFU m(-3) for Serratia and 2420 PFU m(-3) for MS2 page). Sequential flushing resulted in further distribution of micro-organisms into the air although the numbers declined after each flush. Serratia adhering to the sidewalls, as well as free-floating organisms in the toilet water, were responsible for the formation of bacterial aerosols.

CONCLUSIONS: Although a single flush reduced the level of micro-organisms in the toilet bowl water when contaminated at concentrations reflecting pathogen shedding, large numbers of micro-organisms persisted on the toilet bowl surface and in the bowl water which were disseminated into the air by further flushes.

SIGNIFICANCE AND IMPACT OF THE STUDY: Many individuals may be unaware of the risk of air-borne dissemination of microbes when flushing the toilet and the consequent surface contamination that may spread infection within the household, via direct surface-to-hand-to mouth contact. Some enteric viruses could persist in the air after toilet flushing and infection may be acquired after inhalation and swallowing.