People have been “urged to protect themselves and others” after a rise in coronavirus cases in a part of Yorkshire.
New figures show the equivalent of 20 new cases per 100,000 people in Wakefield - up from 14.8 last week.
Public health bosses in the area have a “growing concern” numbers would continue to increase.
“Two large workplace outbreaks” caused the jump, said Anna Hartley, Wakefield’s director of public health.
The latest data, from Public Health England (PHE) for the seven days to 13 July, shows Leicester still has the highest figure in the country with 99.7 per 100,000, although that is a fall from 126.7.
Ms Hartley said the “risk of more localised outbreaks remains” unless people make an effort to slow the spread of infection by social distancing, washing their hands, wearing masks in enclosed spaces and not sharing cars with anyone outside their household.
Wakefield Council said it expected the district to be identified as “an area of concern” following the release of the latest infection figures.
Recent outbreaks found the majority of people testing positive for coronavirus did not display any symptoms, the authority explained.
Ms Hartley said: “We have been closely monitoring the situation in Wakefield, and the wider region, from the start and the recent release of postcode data has helped us to understand the spread of the virus in the district.
“We have effective monitoring in place to map relevant data and spot trends, which acts as our early warning system.
“The increase in case numbers has resulted from two large workplace outbreaks, where workforce testing identified large numbers of asymptomatic cases.”
Earlier this month, 17 people tested positive at Forza Foods in Normanton, while a small number were found to have the virus at an Ossett bed factory.
More than 20 people at accommodation for asylum seekers contracted the virus as well over the past week.