CFD Modelling of Pathogen Transport due to Human Activity

Health-care Associated Infection is a major concern with 1 in 11 patients affected each year.
There is evidence that some pathogens may be transported by an airborne route, and hence fluid
modelling tools, such as Computational Fluid Dynamics (CFD), are increasingly used to aid
understanding of the transport mechanisms of infection. These models tend to only consider
respiratory infections that are released from a single point, such as a person coughing. However
there is substantial evidence that certain pathogens, such as MRS A, may be released from the
skin during regular routine activities (e.g. undressing, walking).
An observational and air sampling study carried out on a respiratory ward found that certain
activities correlated to greatly increased numbers of large particles (> 5µm), and bioaerosols.
The increased concentrations of bioaerosols also corresponded to sampling of potentially
pathogenic Staphylococcus aureus. It is therefore necessary to be able to represent these releases
ofbioaerosols within CFD models used in design and risk assessment.
Bioaerosol transport is modelled in CFD simulations usmg passive scalar transport and
Lagrangian particle tracking models with the DRW model to simulate turbulent diffusion. These
are validated for the first time using spatial variation of airborne and deposited bioaerosols
generated under controlled conditions. Simpler multi-zone models are compared to CFD and
found to perform well at simulating the bioaerosol decay within large spaces that can be
assumed to be well mixed, however they are not refined enough to simulate the detail required
to study the transfer of infection between individual patients.
A zonal source model is introduced and validated with the aim of representing the time average
dispersion from a transient source in a steady state model. This enables the dispersion of
bioaerosols from activities occurring in hospital wards to be represented within CFD models.
The zonal source model is shown to give a good representation of the average dispersion and
total deposition of a transient source, whereas a point source is not. Point sources produce
different dispersion patterns to zonal sources and so it is recommended that both are used to
simulate bioaerosols produced due to activities or respiratory diseases. Point sources are found
to be highly sensitive to the injection position, whereas the zonal source is found to produce
relatively similar patterns of dispersion for varying size definitions.
CFD is a useful tool for studying pathogen transport in indoor spaces, and when doing so it is
recommended that the potential bioaerosol release from the skin is considered which can be
taken into account within a steady state model using a zonal source model.