Real-time bioaerosol analysis in the healthcare environment

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Fennelly, Mehael
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University College Cork
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Airborne infection has been difficult to study in hospitals. Conventional sampling methods for airborne organisms are limited in sample time intervals (minutes to hours) and conventional culture requirements, restricting organism detection and only allowing retrospective analysis (days). This limits their usefulness in analysing air quality and risks of airborne transmission of infection. They provide limited data for standard setting and assessing the effect of interventions designed to increase air quality and decrease airborne infection risks. Direct continuous bioaerosol sampling is an established technology used to characterise ambient external air. Portable instruments such as the Wideband Integrated Bioaerosol Sensor (WIBS) combine laser particle size and shape detection with signals of particle viability (fluorescence from amino acids and NAD(P)H) characteristic of bioaerosols. This aim of this thesis was to investigate the utility of continuous monitoring approaches including WIBS and other instruments to characterise indoor air bioaerosols in hospital environments and evaluate the results of interventions designed to increase air quality. The WIBS-4A was used to characterise airborne biological particles in a 4-bedded hospital respiratory ward bay over a 4-week period before and during a plasma air treatment intervention designed to increase air quality. Twice-daily conventional impaction and settle plates and surface swabs were carried out in parallel with continuous WIBS bioaerosol monitoring. No statistical difference between conventional culture counts was detected during the plasma air treatment period compared with the control. Cumulative continuous monitoring plotted diurnally revealed raw numbers of airborne fluorescent particles were lowest at night, with four striking recurrent fluorescent particle peaks during the daytime when the number of particles increased by over 200-fold compared to the nocturnal minimum. These peaks corresponded to observed nebuliser use on the ward. WIBS analysis of the two nebulised therapy drugs used on the ward defined a characteristic fluorescence signature for nebuliser aerosols. This allowed design of a threshold filter to remove interferent nebulised drugs from fluorescent particle counts which did not eliminate bacteria when applied to experimentally aerosolised bacteria. Both raw and filtered WIBS data (excluding nebulised drug particles) showed a statistically significant ~28% reduction in fluorescent particles, (P<0.05), during the operation of the plasma disinfection unit. The clinical significance of this requires further study. The effect of footfall counts on bioaerosol concentrations was also monitored by deploying an infra-red footfall counter in tandem with the WIBS instrument. Both devices were successful in identifying that the highest footfall count coincided with the highest bioaerosol concentrations observed on the ward, which also coincided with the main morning staff shift change and handover. The cumulative filtered count data was used to devise a statistical threshold which could be the basis of a standard for the environment tested. The WIBS-4A was used in conjunction with the nebulised drug signatures to show that a portable extractor tent (Demistifier 2000, Peace Medical) was 100% efficacious in preventing spread of nebulised bronchodilator drug aerosols. This confirmed that use of Extractor tents prevents spread of drug particles from nebulised therapy. Air DNA samples were taken on six separate days over three months on the respiratory ward, and a preliminary analysis suggested that in most cases the largest single group at Phylum level were Firmicutes (Clostridiaceae/Clostridiales Families). Because these bacteria are potentially of gastrointestinal origin, it was hypothesized the source could be a communal lavatory that was present within the ward bay. A week-long WIBS campaign was therefore undertaken in a communal office toilet to investigate aerosol production from different toilet activities. Increased fluorescent particles were found in lavatory air on flushing after defaecation compared to other activities. Previous studies reporting the effect of toilet lids have found that they prevent the spread of visible droplets on flushing, however the effect on smaller particles was less clear cut. This study found that placing the lid down before flushing the toilet reduced the number of airborne fluorescent particles produced by flushing following defaecation, however it significantly increased particle size, shape, particle fluorescent intensity and residency time of defaecation-related particles in the air. A hypothesis is presented to account for this, involving acoustic reverberation magnification of flush-related turbulence by the lid, and implications of this for toilet design are discussed. This thesis highlights the ability of continuous bioaerosol detection by instruments such as WIBS to provide biologically meaningful characterisation of the healthcare environment. This characterisation facilitates airborne particle source attribution, allows provisional standard setting, and provides a powerful mode of assessment of the results of interventions designed to increase air quality.
Bioaerosol , Light induced fluorescence , WIBS , Air sampling , Airborne
Fennelly, M. 2020. Real-time bioaerosol analysis in the healthcare environment. PhD Thesis, University College Cork.
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