Aside from this outbreak investigation , the evidence presented by other researchers in support of the airborne transmission of norovirus  has been rather inconclusive. In a nosocomial outbreak in Toronto, reported by Sawyer et al. , housekeepers who visited or walked through the emergency room were more likely to become ill than those who did not encounter that area, and patients who visited the emergency room on 11 or 12 November were much more likely to develop infections than those who visited on 8 November. However, these characteristics could also be explained by fomite transmission because the surfaces surrounding the index patients would usually have been more contaminated  and surface contamination would be much more severe at a later stage of the outbreak than at an earlier stage .