the outbreak, eight healthy guinea pigs were exposed to an aerosol of concentrated potable water. Seven animals developed pneumonia due to the Le-l strain of L. pneumophila. In one of these guinea pigs, the Le-l strain was also isolated from the blood and spleen. These results provided support to the theory that exposure of humans to aerosols of potable water contaminated with L. pneumophila may cause legionella pneumonia.17 Again in 1985, Garye Bollin et al 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 to 5 CFU/15 ft3


How Coronavirus is spread through aerosol through the air. ]

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-min sampling periods. A total of 19 paired water and air samples were obtained from 14 hot-water taps. A total of 17 of the water cultures grew L. pneumophila. Two colonies of L. pneumophila (one on stage one, one on stage three) 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 one, five on stage two) 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.18

More recently at the University Hospital of Brussels the incidence of new patients with Carbapenemase-producing Enterobacteriaceae (CPE) rose from one case in 2010 to 35 cases in 2015. Environmental samples suggested that a contaminated washbasin was the

source of the outbreak. Besides other strains, Citrobacter freundii type OXA-48 was frequently isolated from patients and washbasins. To investigate the relationship between those strains, pulsed-field gel electrophoresis was performed. The strains isolated from patients and the washbasin in the implicated room were highly related and pointed to sink-to-patient transmission. In total, 7 of 8 sinks in the isolation rooms of the ICU were found to be CPE contaminated. To control the outbreak, the washbasins and their traps and pipework were replaced with new ones, they were then flushed every morning with a glucoprotamin solution and routines regarding sink practices were improved leading to discontinuation of the outbreak.19

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 Jessen15

who “seeded” several types Loewenstein 4ChAdAug19_Hres.qxp_Loewenstein 2ChAdAug19_Hres 07/06/2019 09:59 Page 1

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.

THE ELISA FAMILY The future of intensive care ventilation

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.

In 2005, Barker et al experimented with toilet bowls and found that 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.21 In 2011 Best et al22

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.

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