Figure 1 gives the number of norovirus positive outbreaks per month for the years 2014-2015. It can be seen that, for 2014, the two-monthly norovirus incidence was low and did not change significantly in the period January-October, but rose significantly in the period November-December. In contrast, in 2015, the two-monthly incidence was low and did not change significantly in January-June, but then rose sharply and remained at a higher level for the rest of the year.