As of Monday, PHE has changed the way it records the location of those who have tested positive for the virus.
The address given when tests are taken will now be used as that person’s area of residence, rather than the address recorded on their NHS record.
PHE said: "Due to reallocation of cases in this way, the number of cases reported by a local authority may be artificially high or low on November 16."
For Wiltshire, this has resulted in a decrease in 255 cases, as back dated from September 1, according to director for public health in Wiltshire, Kate Blackburn.
The seven day rate of infection in Wiltshire now stands at 107 cases per 100,000 people.
This is lower than the infection rate of 190 in the south west and far below the national figure of 273 cases per 100,000 people.