Does spatial proximity drive norovirus transmission during outbreaks in hospitals?

Harris, John P; Lopman, Ben A; Cooper, Ben S; O'Brien, Sarah J

Whilst this might at first seem an obvious finding, there are competing theories about the transmission of the virus in complex healthcare settings. For example transmission might occur through staff transferring virus on their hands or patients touching infected surfaces with their hands when moving around the wards or the hospital. The strength of our conclusion is sensitive to the assumed serial interval distribution. We used values derived from the dates of onset of illness in patients during outbreaks on hospital wards. We also performed sensitivity analysis using a serial interval distribution derived from a study of norovirus in children [13] . However, because the degree to which this generalizes to a hospital setting is unclear (intuitively the high contact rates in hospitals would be expected to lead to shorter serial intervals) [17] we explored serial intervals from 0.5 days to four days, whilst constraining the variance. Our results show that for serial intervals of less than 2 days the observed effect of proximity (sharing a bay with someone else who was ill) is highly F o r p e e r r e v i e w o n l y significant (p < 0.001) and for serial intervals up to 2.5 days remained significant at the 5% level. This pattern was similar whether using the observed serial interval distribution from the outbreak data or using a parametric probability distribution.