Methods Development for Toilet to Evaluate Aerosol Generation

Abstract

• Infectious disease public health exposure may be associated with flush-related aerosols;
• New appropriate and effective methodology should be established to evaluate flush-related aerosol generation;
• A new experimental apparatus was tested;
• The results confirmed that toilet flushing did increase airborne particle concentrations in the bathroom air.

Introduction

• Aerosolized pathogenic microorganisms can be responsible for human respiratory infections.
• Gastroenteritis and norovirus remain the most common aerosolized microorganisms in toilets (Nazaroff, 2011).
• Different methods of research were implemented (Johnson & Lynch, 2008; Johnson et al., 2013).
• Earlier technical challenges justify the need to develop approaches and methods for measuring flush-related bioaerosol generation.

Purpose

The purpose was to develop and test an apparatus and method for measuring aerosol generation related to toilet flushing.

Rationale:

• Questionable validity of earlier findings;
• Bioaerosol transmission leading to disease outbreaks (Johnson et al., 2013);
• The need to reduce the scope of infectious diseases;
• The need to develop new guidelines for preventing airborne infectious diseases.

Literature Review: Aerosol Generation

• Aerosol generation and release have long been a matter of public health concerns (Sanchez-Monedero, Stentiford & Urpilainen, 2005).
• Any public toilet increases the risks of airborne infections.
• The direction of bioaerosolization depends on the physical principles of speed and transport.
• The current methods fail to control the dynamics of virus-laden bioaerosols (Morawska, 2005).

Literature Review: Why Important

• The problem of bioaerosol generation is quite serious.
• Sewage-related bioaerosols can be potentially responsible for SARS.
• Toilet flushing generates major and minor droplets carrying a variety of microorganisms (Johnson et al., 2013).
• Bioaerosolization of toilet flushing cannot be confirmed without effective analytical methods.

Literature Review: Sources of Aerosolized Microorganisms in Toilets

• Toilet flushing is a source and driver of aerosolized microorganisms (Leed, 2011).
• Contact transmission is a result of contamination with flush droplets (Johnson et al., 2012).
• Toilet flushing is a source of E. coli (Gerba et al., 1975), as well as gastroenteritis, Clostridium difficile, and S. Epidermidis (Best et al., 2012; Johnson et al., 2012; Nazaroff, 2011).

Toilet Flushes and Aerosol Generation: Review of Methods

Wallis et al. (1985)

• The researchers detected human enteric viruses from aerosols by using filterite filters and glycine buffer;
• Even with the air flowing at 100 liters per minute, no virus passed the filter.

Johnson and Lynch (2008)

• The researchers tested an analytical method for counting particles;
• The method proved to be effective enough to measure the number of surrogate bioaerosol particles.

Methods and Materials: Variables

• Purpose: To develop and test an apparatus and method for measuring aerosol generation associated with toilet flushing.
• Independent variable: toilet flush.
• Dependent variable: particles concentration.

Instrumentation

• Clear cylindrical 4-feet tall, 18-inches high wide plastic chamber.
• HEPA filtration system.
• Holmes ®True | HEPA Allergen Remover.
• Model 3321 Aerodynamic Particle Sizer® Spectrometer.
• Renegair® pump.

Setting

The experiment was conducted in two half and one full residential standard bathrooms.

Both bathrooms were equipped with 1.6 GPF (6.0 LPF) toilets.

Procedure

Divided into two stages;

• The first was used to confirm that toilet flushing leads to aerosol generation;
• The second was used to test the efficacy of the proposed method for measuring bioaerosolization in toilets.
• Basic Lysol cleaner was used to reduce background particles.
• The chamber was 4 feet tall and 18 inches wide;
• HEPA air intake filters were on all sides;
• The HEPA exhaust/vacuum filter was located on the top of the chamber;
• The sampling port was connected to the APS monitor with the help of a tube (1 inch in diameter, 40 inches long).

Experiment

• Bathrooms were sealed with duck tapes;
• Holmes® Allergen Remover was switched to run 30 minutes before toilet flushing;
• Three toilet flushes were initiated with a one-minute interval;
• TSI Aerodynamic Particle Sizer 3321 was used to measure aerosol generation after each flush.

Experiment: Graphics

Procedure, Sample, and Toilet Seeding

• The Regenerative Pump was used to filter the air out of the chamber;
• Medium duty white caulk gum was used as a gasket between the toilet bowl rim and the chamber;
• Samples were collected every minute, during 1 hour (60 minutes);
• Toilet seeding was used to imitate human excretion.

Clear Cylindrical Air-Tight Chamber

Data Analysis

• Statistical analyses;
• Basic Excel and STATA;
• Two sample t-tests, unequal variances, and mean differences between total counts;
• Individual particle sizes.

Results

Experiment 1, Toilet 1

• Flushing generates aerosols;
• 133.4 particles/cm3, SD 72.2 with flushing against 42.9 particles/cm3, SD 7.8 without flushing.

Experiment 2, Toilet 1

• seeded with 0.05 µm polystyrene beads;
• flushing leads to an increase in particle counts;
• 177.9 particles/cm3, SD 162.3 with flushing against 50.1 particles/cm3, SD 14.9 without flushing.

Experiment 3, Toilet 1

• Results are similar to Experiment 1 without seeding;
• Individual particle counts are lower than in Experiment 1;
• Patterns of changes are similar to Experiment 1.

Experiment 4, Toilet 2

• Different bathroom;
• No seeding;
• Flushing generated aerosols;
• 107.6 particles/cm3 with flushing against 30.1 particles/cm3 without it.

Discussion

• The results confirm those of Johnson et al. (2013);
• It is the first study to use a TSI Aerodynamic Particle Sizer for changes in particle counts;
• All four experiments confirm that toilet flushing leads to an increase in particle counts;
• Changes in particle counts are related to their size.

Limitations and Recommendations

Limitations

• The experiments were conducted in household toilets;
• The air pumped in and out of the chamber could contribute to changes in aerosolized particle counts;
• Polystyrene beads were used to imitate seeding.

Recommendations

• Future studies are needed to understand the relationship between particle counts and size.

References

Best, E.L., Sandoe, J.A.T. & Wilcox, M.H. (2012). Potential for aerosolization of Clostridium difficile after flushing toilets: The role of toilet lids in reducing environmental contamination risks. Journal of Hospital Infection, 80(1), 1-5.

Gerba, C.P., Wallis, C. & Melnick, J.L. (1975). Microbiological hazards of household toilets: Droplet production and the fate of residual organisms. Applied Microbiology, 30(2), 229-237.

Johnson, D.L. & Lynch, R.A. (2008). An efficient analytical method for particle counting in evaluating airborne infectious isolation containment using fluorescent microspheres. Journal of Occupational and Environmental Hygiene, 5(4), 271-277.

Johnson, D.L., Mead, K.R., Lynch, R.A. & Hirst, D.V. (2013). Lifting the lid on toilet plume aerosol: A literature review with suggestions for future research. American Journal of Infection Control, 41(3), 254-258.

Johnson, D., Lynch, R., Marshall, C., Mead, K. & Hirst, D. (2013). Aerosol generation by modern flush toilets. Aerosol Science and Technology, 47(9), 1047-1057.

Leed, S.W. (2011). Solving indoor airborne disease transmission problems. Engineered Systems, 56-61. Web.

Morawska, L. Droplet fate in indoor environments, or can we prevent the spread of infection?, in Yang,X., Zhao, B.,& Zhao, R. (Eds.) Proceedings of Indoor Air 2005 : the 10th International Conference on Indoor Air Quality and Climate, Springer, Beijing, China, pp. 9-23.

Nazaroff, W.W. (2011). Norovirus, gastroenteritis, and indoor environmental quality. Indoor Air, 21(5), 353-356.

Sanchez-Monedero, M.A., Stentiford, E.I. & Urpilainen, S.T. (2005). Bioaerosol generation at large-scale green waste composting plants. Journal of Air & Waste Management, 55(5), 612-618.

Wallis, C., Melnick, J.L., Rao, V.C. & Sox, T.E. (1985). Method for detecting viruses in aerosols. Applied and Environmental Microbiology, 50(5), 1181-1186.