Wellington is struggling to shake its crypto outbreak

There have been 81 confirmed cases of the contagious gastro bug in the Greater Wellington Region this year - double what it was during the same period last year.

The outbreak, said to be linked to public swimming pools, is spreading through households, schools, and early childhood centres.

Central region medical officer of health Dr Craig Thornley says around two thirds of cases are in the Hutt Valley area.

He says people need to wash their hands with soap and avoid the pool for two-weeks after symptoms end to prevent further spread.