Seventy-eight confirmed norovirus outbreaks have been reported in institutions in the past three months, affecting 908 people.

The Centre for Health Protection today said the figures are up on the 57 outbreaks recorded in 2006, the 22 reported in 2007 and 16 in 2008.

The centre's Public Health Laboratory Service Branch has detected a new recombinant 2006-08 strain of norovirus, which has also been detected in other countries in 2009. However, there is so far no evidence suggesting these genetic changes are associated with more severe illness.

Norovirus undergoes genetic changes from time to time, at about two- to three-year intervals. In Hong Kong, new strains of norovirus were also detected in 2002, 2004 and 2006.

The centre issued letters to healthcare professionals and institutions in November alerting them to the seasonal rise in norovirus activity and to provide health advice.