Modelling infection risk due to environmental contamination in hospital single and multi-bed ward accommodation

This research considers whether hospital single rooms are better than multi-bed accommodation
at reducing the risk of healthcare-acquired infections. The focus is to provide
a mathematical model which quantifies the contamination levels of healthcare workers’
(HCW) hands from surfaces within rooms. This is achieved through a multidisciplinary
approach involving computational fluid dynamics (CFD) and biological experimental techniques
coupled with clinical observation and Markov Chain Monte-Carlo modelling.
Spatial deposition of aerosolised bacteria was measured in a test room under different
layouts: An empty room, a single-bed and a two-bed room. Comparison with CFD
demonstrates realistic predictions of spatial deposition, and a Reynolds Stress turbulence
model yields superior results compared to other models.
An observational study of patient care at aWelsh hospital showed that hand hygiene choice
and frequency varied strongly. HCWs performing short episodes of care had a predilection
for alcohol rub. In other care types the usage of alcohol rub or soap and water was 50/50.
HCW surface contact patterns in rooms were modelled by a Markov chain and fed into
a mathematical model to calculate the pathogen colonisation level on hands after patient
care. A parametric study highlights the differences between care type and colonisation.
Results indicate that hand hygiene carried out by nurses may need to be rethought.
The model was applied using CFD predicted spatial contamination levels, in both multibed
and single rooms. When ventilation rates were equal, hand colonisation differences
were small. Results demonstrate that this depends on care type, the number of surface
contacts and in particular on the distribution of surface pathogens. Contamination on
the HCWs’ hands decreases monotonically after care in single rooms; however increases
during contact with subsequent patients in multi-bed rooms. Enforcing hand hygiene due
to the knowledge of an infectious patient makes single rooms significantly less risk prone.