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Background More evidence is emerging on the role of surface decontamination for reducing hospital-acquired infection (HAI). Timely and adequate removal of environmental pathogens leads to measurable clinical benefit in both routine and outbreak situations. Objectives This systematic review aimed to evaluate published studies describing the effect of automated technologies delivering hydrogen peroxide (H202) or ultra-violet (UV) light on HAI rates. Methods A systematic review was performed using relevant search terms. Databases were scanned from January 2005 to March 2020 for studies reporting clinical outcome after use of automated devices on healthcare surfaces. Information collected included device type, overall findings; hospital and ward data; study location, length and size; antimicrobial consumption; domestic monitoring; and infection control interventions. Study sponsorship and duplicate publications were also noted. Results While there are clear benefits from non-touch devices in vitro, we found insufficient objective assessment of patient outcome due to the before-and-after nature of 36 of 43 (84%) studies. Of 43 studies, 20 (47%) used hydrogen peroxide (14 for outbreaks) and 23 (53%) used UV technology (none for outbreaks). The most popular pathogen targeted, either alone or in combination with others, was Clostridium difficile (27 of 43 studies: 63%), followed by methicillin-resistant Staphylococcus aureus (MRSA) (16 of 43: 37%). Many owed funding and/or personnel to industry sponsorship (28 of 43: 65%) and most were confounded by concurrent infection control, antimicrobial stewardship and/or cleaning audit initiatives. Few contained data on device costs and rarely on comparable costs (1 of 43: 2%). There were expected relationships between the country hosting the study and location of device companies. None mentioned the potential for environmental damage, including effects on microbial survivors. Conclusion There were mixed results for patient benefit from this review of automated devices using H202 or UV for surface decontamination. Most non-outbreak studies lacked an appropriate control group and were potentially compromised by industry sponsorship. Concern over HAI encourages delivery of powerful disinfectants for eliminating pathogens without appreciating toxicity or cost benefit. Routine use of these devices requires justification from standardized and controlled studies to understand how best to manage contaminated healthcare environments.

Mathematical models describing indirect contact transmission are an important component of infectious disease mitigation and risk assessment. A model that tracks microorganisms between compartments by coupled ordinary differential equations or a Markov chain is benchmarked against a mechanistic interpretation of the physical transfer of microorganisms from surfaces to fingers and subsequently to a susceptible person's facial mucosal membranes. The primary objective was to compare these models in their estimates of doses and changes in microorganism concentrations on hands and fomites over time. The abilities of the models to capture the impact of episodic events, such as hand hygiene, and of contact patterns were also explored. For both models, greater doses were estimated for the asymmetrical scenarios in which a more contaminated fomite was touched more often. Differing representations of hand hygiene in the Markov model did not notably impact estimated doses but affected pathogen concentration dynamics on hands. When using the Markov model, losses due to hand hygiene should be handled as separate events as opposed to time-averaging expected losses. The discrete event model demonstrated the effect of hand-to-mouth contact timing on the dose. Understanding how model design influences estimated doses is important for advancing models as reliable risk assessment tools.

Finding a non-pathogenic surrogate aerosol that represents the deposition of typical bioaerosols in healthcare settings is beneficial from the perspective of hospital facility testing, general infection control and outbreak analysis. This study considers aerosolization of dilute aqueous lithium chloride (LiCl) and sodium chloride (NaCl) solutions as surrogate tracers capable of representing Staphylococcus aureus bioaerosol deposition on surfaces in mechanically ventilated rooms. Tests were conducted in a biological test chamber set up as a replica hospital single patient room. Petri dishes on surfaces were used to collect the Li, Na and S. aureus aerosols separately after release. Biological samples were analyzed using cultivation techniques on solid media, and flame atomic absorption spectroscopy was used to measure Li and Na atom concentrations. Spatial deposition distribution of Li tracer correlated well with S. aureus aerosols (96% of pairs within a 95% confidence interval). In the patient hospital room replica, results show that the most contaminated areas were on surfaces 2 m away from the source. This indicates that the room’s airflow patterns play a significant role in bioaerosol transport. NaCl proved not to be sensitive to spatial deposition patterns. LiCl as a surrogate tracer for bioaerosol deposition was most reliable as it was robust to outliers, sensitive to spatial heterogeneity and found to require less replicates than the S. aureus counterpart to be in good spatial agreement with biological results.

Simulation of urban airflow and ventilation potential is desirable for building design, however the\ud complex and transient nature of flows in urban environments makes this a challenging task. This study\ud aims to evaluate the capability of a lattice-Boltzmann method (LBM) code deployed on a graphical\ud processing unit (GPU) using a large eddy sub-grid turbulence model for cross-flow ventilation of an\ud idealised cubical building at wind-tunnel scale. ANSYS Fluent is used as a numerical comparison. Façade\ud pressure and ventilation of the cube are investigated for parallel and perpendicular wind directions with\ud the building in isolation and regular array format. Pressures, velocities and ventilation rates are\ud compared to experimental data from wind tunnel and full-scale experiments of the Silsoe cube. Simulations\ud compare favourably with experimental values and between each other. When the cube was\ud surrounded by other cubes, simulations suggest that vortex shedding from up-wind buildings provides\ud pulsating ventilation, improving airflow ingress in the parallel wind cases. A parametric study showed\ud that doubling surrounding building height had a small negative effect on ventilation but was mitigated\ud by high levels of downdraft and flow fluctuations in the vertical plane. Comparatively, doubling the\ud central building height had a net positive effect but caused high internal airspeeds for both angles. The\ud LBM code running on one GPU was several orders of magnitude faster than Fluent with similar accuracy.\ud Simulation time using the LBM approach was several orders of magnitude lower than Fluent.

Building location and orientation with respect to incident wind angle are important parameters in determining wind-driven natural ventilation. Experimentally measured façade pressures and ventilation rates in the Silsoe cube under single-sided and cross-flow ventilation configurations are compared with CFD simulations conducted in OpenFoam and ANSYS Fluent using a typical linear workflow approach. Eight wind directions are studied with the cube in isolation and in a new staggered nine cube array format. Comparison is made using CIBSE's prescribed ventilation calculation method based on internal/external building pressure differences. Ventilation rate in the isolated cube with single-sided opening was comparatively lower than either of the cross-flow cases, and relationships between air change rate and wind angle were much weaker in the array cases. For the single opening case with the isolated cube, ventilation effectiveness decreases as the wind turns towards the opening due to increased short-circuiting of airflows. Turbulent structures close to windows improve mixing in the array case. Simulations suggest that vortex shedding from up-wind buildings provides pulsating ventilation in both window configurations, which may attenuate the negative effects of upwind flow obstruction.

This study considers air exchange between outdoor and indoor environments in the context of a hospital room with single-sided natural ventilation. Computational fluid dynamics (CFD) simulations are used to examine the trade-off between outdoor pollutant ingress and indoor contaminant dilution, and the influence of the street canyon design. Two street-canyon aspect ratios were investigated (Height/Width=0.5 and 1) with roof angles of zero and 26.6º. An open window was located on the on the leeward side connecting to an interior room. ANSYS Fluent 15 was used to model airflow in the indoor and outdoor spaces and employed a k-omega turbulence model. A tracer was released in the outdoor location between the buildings and concentrations determined inside the open window. A second tracer released inside the building was used to establish concentrations at the pedestrian level outside. Increasing canyon width reduced the residence time of the outdoor pollutant and reduces ingress. Flat roofs for both ratios drew the tracer to the leeward side of the building due to negative pressures. However, pitched roofs created more complex systems that reduced contaminant in the canyon due to unsteady vortices. Contaminants released inside the room result in proportionally higher concentrations outside for narrow canyons.