This ~7kb RNA virus causes a large proportion of viral gastro-enteritis worldwide and leads to seasonal outbreaks of vomiting and diarrhoea in hospitals. In closed communities such as cruise ships, large numbers of cases close in space and time are likely to be true outbreaks – however, in hospitals it is less clear whether such persisting clusters are caused by ongoing transmission (from a “super-spreader”, environmental contamination or failure to contain successive transmissions within the hospital) or, given ward movements and visitors, whether they arise from repeated re-introductions of new strains from the wider community (a series of independent, limited outbreaks). The difference is critical, since the respective most appropriate control strategies differ: eg, closure and extensive decontamination of infected wards versus local decontamination and simple cohorting of cases.

Local population-based sampling and increased resolution from sequencing the whole of the viral genome will increase the ability to distinguish ongoing point source transmission from re-introductions. Whole genome sequencing has the potential to improve outcomes for individual patients admitted to hospital, by determining whether a persistent Norovirus outbreak is actually occurring (and therefore more stringent isolation procedures are required) and whether multiple outbreaks are in fact caused by the same strain (in which case merging cohorts could free beds for other patients and prevent specialist wards such as stroke units being closed to new admissions).

Our work

Our group took the samples, and sequenced the norovirus genome. We found that instances when, despite patients in adjacent beds both developing norovirus at similar times, they appear to have got it from different sources – thought to be family or visitors who had the infection in the community.

This gives us crucial information about how to manage norovirus in the hospital – not only is isolation and cleaning important, but so is preventing people with norovirus from visiting the hospital.