Review: the use of real-time fluorescence instrumentation to monitor ambient primary biological aerosol particles (PBAP)

Primary biological aerosol particles (PBAP) encompass many particle types that are derived from several biological kingdoms. These aerosol particles can be composed of both whole living units such as pollen, bacteria, and fungi, as well as from mechanically formed particles, such as plant debris. They constitute a significant proportion of the overall atmospheric particle load and have been linked with adverse health issues and climatic effects on the environment. Traditional methods for their analysis have focused on the direct capture of PBAP before subsequent laboratory analysis. These analysis types have generally relied on direct optical microscopy or incubation on agar plates, followed by time-consuming microbiological investigation. In an effort to address some of these deficits, real-time fluorescence monitors have come to prominence in the analysis of PBAP. These instruments offer significant advantages over traditional methods, including the measurement of concentrations, as well as the potential to simultaneously identify individual analyte particles in real-time. Due to the automated nature of these measurements, large data sets can be collected and analyzed with relative ease. This review seeks to highlight and discuss the extensive literature pertaining to the most commonly used commercially available real-time fluorescence monitors (WIBS, UV-APS and BioScout). It discusses the instruments operating principles, their limitations and advantages, and the various environments in which they have been deployed. The review provides a detailed examination of the ambient fluorescent aerosol particle concentration profiles that are obtained by these studies, along with the various strategies adopted by researchers to analyze the substantial data sets the instruments generate. Finally, a brief reflection is presented on the role that future instrumentation may provide in revolutionizing this area of atmospheric research

Portable HEPA Filtration Successfully Augments Natural-Ventilation-Mediated Airborne Particle Clearance in a Legacy Design Hospital Ward

As the severe acute respiratory syndrome coronavirus-2 pandemic has proceeded, ventilation has been recognized increasingly as an important tool in infection control. Many hospitals in Ireland and the UK do not have mechanical ventilation and depend on natural ventilation. The effectiveness of natural ventilation varies with atmospheric conditions and building design. In a challenge test of a legacy design ward, this study showed that portable air filtration significantly increased the clearance of pollutant aerosols of respirable size compared with natural ventilation, and reduced spatial variation in particle persistence. A combination of natural ventilation and portable air filtration is significantly more effective for particle clearance than either intervention alone

Real-time bioaerosol analysis in the healthcare environment

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