People have been “urged to protect themselves and others” after an increase in coronavirus cases in part of Yorkshire.
New figures show the equivalent of 20 new cases per 100,000 people in Wakefield – up from 14.8 last week.
The bosses of public health in the region have a “growing concern”, the number would continue to increase.
“Two major epidemics in the workplace” caused the jump, said Anna Hartley, director of public health for Wakefield.
The latest data, from Public Health England (PHE) for the seven days to July 13, shows that Leicester still has the highest figure in the country at 99.7 per 100,000, although this is down from 126.7.
Hartley said the “risk of more localized outbreaks remains” unless people make an effort to slow the spread of infection through social distancing, wash their hands, wear masks in confined spaces and do not share cars with anyone outside their home.
Wakefield Council said it expected the district to be identified as “an area of concern” after the release of the latest infection figures.
Recent epidemics have revealed that the majority of people who test positive for the coronavirus have no symptoms, the authority said.
Hartley said: “We have been monitoring the situation in Wakefield and the wider region from the start and the recent release of postal code data has helped us understand the spread of the virus in the district.
“We have put in place effective monitoring to map relevant data and spot trends, which is our early warning system.
“The increase in the number of cases is the result of two large epidemics in the workplace, where staff testing has identified a large number of asymptomatic cases. ”
Earlier this month, 17 people tested positive at Forza Foods in Normanton, while a small number had the virus at an Ossett bed factory.
More than 20 people housed by asylum seekers have also contracted the virus in the past week.