New norovirus strain, Sydney 2012, may be linked to increased activity
A recent Eurosurveillance report notes that molecular data shared through the NoroNet (surveillance system) network suggest that this increase is related to the emergence of a new norovirus genotype II.4 (GII.4) variant, termed Sydney 2012.
In the UK, the Health Protection Agency (HPA) says molecular testing carried out when norovirus cases started to rise in October revealed a cocktail of different strains that were circulating including Sydney 2012 and another called New Orleans 2009, although no one strain was dominant, according to an HPA press release today.
However, the latest testing of the most recent outbreaks, completed this week, has now shown that Sydney 2012 has overtaken all others to become the dominant strain. The first report of this variant was from Australia in March 2012.
In recent history, strains belonging to norovirus (NoV) GII.4 have been responsible for the majority of outbreaks, as well as community cases of acute gastroenteritis. It has been suggested that hospitalization and deaths occur more frequently during peak seasons associated with new NoV GII.4 variants. These epidemic variants of GII.4 have emerged every two to three years, according to the Eurosurveillance report.
This new norovirus strain does not cause more serious illness than others and the methods of managing cases and outbreaks are the same for any strain of norovirus, according to the HPA.
Dr David Brown, Director of Virology Reference Department at the HPA said, “It is always difficult to predict the norovirus season and this year is no different.
“Noroviruses mutate rapidly and new strains are constantly emerging. At the start of the season it is normal for outbreaks to be caused by a range of different strains. However as the season progresses particular strains are more successful and become dominant. The emergence of a new strain does not mean that it causes more serious illness and managing outbreaks and those will the illness remains the same.”
Although initial data suggests that the late 2012 increase in norovirus activity is a result of the new variant strain, researchers in the Eurosurveillance report conclude that more data is needed to confirm the association between a higher NoV incidence and the new NoV GII.4 2012 variant.
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