Figure 1 shows the monthly occurrence of outbreaks for
the year 2010-11. The trend of positive outbreaks was
higher in the months of winter and late spring, while it was
lower in summer and autumn. The larger number of outbreaks
was observed between November and April. The
temporal occurrence of outbreaks was also examined for
each serotype. Serotypes O and A showed a similar trend,
whilst outbreaks of serotype Asia-1 occurred more in
spring and late autumn (Fig. 1).