Norovirus, the leading cause of infectious gastroenteritis (vomiting & diarrhoea), is currently showing increased activity in Australia, France, the Netherlands, New Zealand, Japan, and the UK.
Genetic analysis of the virus has shown that this has been caused by the emergence of a new strain of norovirus.
The new norovirus genotype II.4 variant, named Sydney 2012 after the place where it was first reported, is related to existing strains Apeldoorn 2007 and New Orleans 2009, but is different enough that there may be limited immunity in the population.