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WATER SYSTEM SAFETY


environmental influences such as humidity, air flow, and temperature. Aerosols, which are responsible for the transmission of airborne micro-organisms by air, consist of small particles named droplet nuclei (1–5 µm) or droplets (>5 µm). Droplet nuclei can stay airborne for


hours, transport over long distances and contaminate surfaces by falling down. In a review article from 2006 the authors found for SARS-CoV-1 that ‘particles of diameters 1–3 µm remained suspended almost indefinitely, 10 µm took 17 minutes, 20 µm took four minutes, and 100 µm took ten seconds to fall to the floor’.5 The article notes that aerosol


transmission is a well known and important exposure pathway for infectious agents such as influenza and other viruses including coronaviruses. SARS-CoV-1 viral RNA was found in air samples, and long range aerosol transport was implicated as the cause of the spread of the disease in several studies. It has been proven that droplets can


contaminate surfaces in a range of over two metres.7


The droplets are also capable


of penetrating deep into the lungs, offering a potential route of infection.8 The susceptibility of acquiring an infectious agent is determined by factors such as: virulence; dose; and pathogenicity of the micro-organism; and the host’s immune response.8–10


Humans generate


bio-aerosols by talking, breathing, sneezing or coughing.6 Based on the infectious status of a person, the bio-aerosols can contain pathogens including influenza,11,12 Mycobacterium tuberculosis,8 Staphylococcus aureus, Varicella zoster virus, Streptococcus spp. or Aspergillus spp.12


Moreover, bio-aerosols can be


generated by devices such as ventilation systems, showers, taps and toilets. Showers and tap water are also able to spread environmental microbes such as Legionella spp.9,10,13 It is now commonly accepted that


bio-aerosols containing harmful pathogens are very much a common and serious contributor to healthcare-acquired infections but are these connections new and what was known of such threats in the past?


In 1985 Bollin et al.15 conducted an air


sampling test in showers and sink areas at the Youngstown Hospital A total of two paired water and air samples were obtained from each of the two shower rooms. All four water cultures grew L. pneumophila. Low numbers of aerosolised L. pneumophila (3-5 cfu/15 ft3


[0.43 m3 ] of air) were


recovered when the air was sampled above the shower doors with the six-stage sampler. Equal numbers of organisms were recovered in the first and second 15-minute sampling periods. A total of 19 paired water and air samples were obtained from 14 hot-water


IFHE DIGEST 2021


In 2011 Best et al16


performed in-situ


testing, using faecal suspensions of C. difficile to simulate the bacterial burden found during disease, to measure C. difficile aerosolisation. They also measured the extent of splashing occurring during flushing of two different toilet types commonly used in hospitals. Their findings were as follows:


C. difficile was recoverable from air sampled at heights up to 25 cm above the toilet seat. The highest numbers of C. difficile were recovered from air sampled immediately following flushing, and then declined eightfold after 60 minutes and a further threefold after 90 minutes. Surface contamination with C. difficile


Example of an Angel Guard washbasin designed to limit the risk of aerosol and splashing.


taps. A total of 17 of the water cultures grew L. pneumophila. Two colonies of L. pneumophila (one on stage 1, one on stage 3) were recovered from air around one of the three taps tested with the six- stage unit. A total of 11 colonies were recovered (six on stage 1, five on stage 2) from five of the remaining 13 taps tested with the two-stage unit. All positive air cultures from the two-


stage unit were obtained during the period when the tap water was running. None were ever obtained before the tap water was turned on or after it was turned off. No air cultures were positive more than once among the rooms that were tested two and three times. Showers, taps and washbasins are not the only means of transmission via aerosol. Toilet flushing is another large risk area. Bio-aerosol production during toilet flushing was first reported in the 1950s by Jessen14


who ‘seeded’ several types


of toilets with Serratia marcescens (then termed Bacillus prodigiosus) and measured bio-aerosols produced by flushing. Agar-filled ‘settle plates’ caught bio-aerosols that fell out of the air because of gravity, and a Bourdillon slit impactor collected air samples. Cistern- fed, gravity-flow toilets and a mains-fed pressure-valve toilet were examined. In addition to colonies found on the floor-based settle plates, microbes were still being captured from the air eight minutes after the flush, indicating collection of ‘droplet nuclei’ bio-aerosols. Droplet nuclei are the tiny particles that remain after the water in a droplet evaporates. They have negligible settling velocity and will float with natural air currents. Jessen observed that the amount of bio-aerosol increased with increasing flush energy.


occurred within 90 minutes after flushing, demonstrating that relatively large droplets are released which then contaminate the immediate environment. The mean numbers of droplets emitted upon flushing by the lidless toilets in clinical areas were 15-47, depending on design. C. difficile aerosolisation and surrounding environmental contamination occur when a lidless toilet is flushed. They concluded that lidless


conventional toilets increase the risk of C. difficile environmental contamination, and they went onto suggest that their use should be discouraged, particularly in settings where C. difficile is common. Unfortunately, despite these findings, it is still common practice in UK healthcare that toilets within clinical areas have no lid and the aerosol created continues to create a risk of infection within a healthcare environment. It has also been found that the use of


hand dryers, especially the increasingly common jet air dryers might have the potential for increasing the risk of aerosols. In a recent study undertaken by Best et al17 it concluded that multiple examples of significant differences in surface bacterial contamination, including by faecal and antibiotic-resistant bacteria, were observed, with higher levels when jet air dryers were present versus paper towel in washrooms.


Water from a tap produces significant aerosol dispersal.


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