Faucet aerator design influences aerosol size distribution and microbial contamination level
Graphical abstract
Introduction
Opportunistic pathogens (OPs) represent a global challenge in healthcare facilities, especially in neonatal intensive care units (NICUs) where they are responsible for nosocomial infections (Fontela et al., 2012; Hewitt et al., 2013; Lake et al., 2018). Infants in NICUs are highly vulnerable and at risk of infection due to several factors such as low birth weight, low gestational age, intravenous therapies and length of stay (Auriti et al., 2003; Christina et al., 2015; Kawagoe et al., 2001). Healthcare associated infections are linked to a high rate of mortality and morbidity, prolonged hospital stays and increased cost of hospitalization (Hornik et al., 2012; Stoll et al., 1996).
In the hospital environment, OPs transmission to patients can occur through several vectors. The sink environment is suspected as the starting point of different routes of transmission for waterborne pathogens, due to their presence in the biofilm and in water (El-Liethy et al., 2020; LeChevallier et al., 1987; McBain et al., 2003; Rogers et al., 1994; van der Wende et al., 1989). A biofilm is a structured cluster of microbial cells surrounded by a matrix of extracellular polymers such as polysaccharides, proteins, nucleic acids and others. It offers protection, resistance to antimicrobial agents and access to nutrients for the microorganisms (Percival et al., 2000). Variable water flow through the pipes can result in bacterial detachment from the biofilm into the water, enabling their dispersion in the environment (Bédard et al., 2018; Lautenschlager et al., 2010; Lehtola et al., 2006). Biofilms present in sink drains (El-Liethy et al., 2020; Hemdan et al., 2019; McBain et al., 2003), make them important OPs reservoirs and reported sources of hospital outbreaks (Bedard et al., 2015; Hota et al., 2009; Kotsanas et al., 2013; Lalancette et al., 2017; Roux et al., 2013). The water in the drain can become a vector of contamination if there is splashing during hand washing, causing retrograde contamination of the faucet aerator and of the surrounding surfaces. The faucet aerator has also been linked to several hospital outbreaks, especially for Pseudomonas aeruginosa (Knoester et al., 2014; Lv et al., 2019; Takajo et al., 2020; Walker et al., 2014; Weber et al., 1999).
Aerators are located at the end of most faucets and are used for different reasons: water conservation, reduced splashing and gentler flow. There is a variety of aerator models on the market with different characteristics such as water flow rate, materials and stream types. Common aerators produce mainly three stream types: aerated, spray and laminar. In the latter two types of flow, there are no air bubbles in the water jet and such aerators should be considered as “flow restrictors” rather than “aerators”. When openings in the aerator allow air to be entrained in the water (aerated stream), bubbles can burst into droplets as they reach the air-water interface. Instabilities at the jet free surface can also result in formation of droplets (Marmottant and Villermaux, 2004). Two transmission routes are commonly defined for droplet containing bacteria: droplet and airborne transmission. Traditionally, droplets with a diameter below 5 μm or 10 μm are considered to evaporate rapidly and result in airborne transmission, also often simply referred to as aerosol transmission. Larger droplets will drop to the ground before evaporation can occur (Siegel et al., 2007; Wells, 1934; World Health Organization, 2014). When the water of a droplet is mostly evaporated, small droplet nuclei form and their content (e.g. bacteria) can potentially remain in the air for an extended period of time (hours) and present a risk for occupants far from the contamination source (Bernards et al., 1998; Fusch et al., 2015; Park et al., 2013; Rutala et al., 1983; Wainwright et al., 2009). The survival of pathogens in aerosol particles will be influenced by environmental factors such as temperature, relative humidity, ultraviolet light exposure and atmospheric pollutants (Ehrlich et al., 1970; Ko et al., 2000; Lighthart, 1973). Larger droplets will fall faster (seconds), limiting the risk of airborne transmission but presenting a source of contamination for the surfaces near the sink. The distinction between these two types of transmission routes is not as well defined as the airborne/droplet dichotomy would suggest. The size cut-off between the two modes of transmission will depend on the aerosol formation mechanism, the pathogens present within the droplet and the environmental conditions such as relative humidity and ambient temperature (Wells, 1934; World Health Organization, 2014). Aerosol-mediated pathogen transmission ultimately depends on patient exposure, with particle size smaller than 5 μm able to reach the lungs and alveoli (Andersen, 1958; Brown et al., 1950; Fernández Tena and Casan Clarà, 2012; Haughney et al., 2010) and susceptible to cause diseases or infections if they contain an infectious dose of a pathogenic organism (Pourchez et al., 2017). Although aerators are suspected as sources of infection in hospitals, very few studies have done direct measurement of aerosols and how they could be a vector of colonisation and infection of patients. Previous studies have measured the production of contaminated droplets and aerosol particles originating from the sink trap during faucet usage. Results showed droplets as a more important vector than aerosol for dispersion of pathogens within the sink trap (Fusch et al., 2015; Hota et al., 2009; Kotay et al., 2019). However, the focus was on contaminated sink drains, with the water flowing from the faucet and aerator not considered as a source of contamination in those studies. The characterisation of aerosol production and aerosol pathogen loads for different types of aerators is therefore critical to determine their role in the transmission of OPs.
The main objective of this study is to quantify the hazard associated with the production of contaminated aerosols from different faucet aerator models currently used in hospitals. The parameters of interest are the number of aerosol particles produced, their size distribution and their contamination level. Salted water is used for a precise measurement of aerator propensity to generate aerosols while water seeded with bacteria is used to provide the aerosols pathogen load. Identifying aerator types that generate less contaminated aerosols will contribute to mitigate the risk associated with the aerator mediated transmission from faucets. This study is part of a large initiative aiming to reconfigure the sink environment to limit transmission of MDR OPs in health care facilities.
Section snippets
Aerator selection
Faucet aerators were selected based on the results of a survey shared with all Directors of Technical Services in November 2018 by the Ministère de la Santé et des Services Sociaux (Health ministry) of Québec. Hospitals and health care facilities were asked to provide information about the manufacturer, model, maximum flow and size of the different faucet aerators used in their facilities. Eight technical service groups responded, 25 aerator models were documented and ten were selected for the
Size distribution
The particle size distribution of the aerosol particles produced by different models of aerators was evaluated using the particle spectrometer at various positions relative to the flow with a 10% (w/v) KCl solution. The highest cumulative number of particles produced was observed at the point where R = 10 mm and z = 150 mm. Preliminary testing showed that the number of particles generated increased as the sampling point was moved closer radially to the water stream, although we did not
Conclusion
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Aerosol particle size distribution and mean mass distribution varied depending on the different models of aerators. New aerators with no aerated jet (models #5, 6 and 9) and the laminar flow aerator (model #8) produced the lowest numbers and mass of aerosols particles when measured with spectrometry. Wide differences in the potential production of aerosol particles were observed between the 6 models of aerated aerators.
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Of the 10 aerator models tested, a new aerator with a low flow, no air inlet
CRediT authorship contribution statement
Marie-Ève Benoit: Investigation, Formal analysis, Validation, Writing – original draft. Michèle Prévost: Funding acquisition, Resources, Supervision, Writing – review & editing. Antonella Succar: Software, Formal analysis, Writing – original draft. Dominique Charron: Writing – review & editing. Eric Déziel: Funding acquisition, Resources, Writing – review & editing. Etienne Robert: Funding acquisition, Resources, Supervision, Writing – review & editing. Emilie Bédard: Funding acquisition,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank Mélanie Rivard, Yves Fontaine, Julie Philibert, Jacinthe Mailly, Marie-Christine Groleau, Charles-Olivier Poirier, Dominic Rivest. This study was supported by a Collaborative Health Research Project Grant, a joint initiative between the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Institutes of Health Research (CIHR).
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