Authorities in the English town of Blackburn have imposed new restrictions on social mingling amid what they say is a “rising tide” of new coronavirus cases.

Director of Public Health Dominic Harrison says Blackburn’s infection rate is 47 per 100,000 people, one of the highest in the country.

He said Wednesday that the main issue is transmission within families, mostly in South Asian households. He told the BBC that “what we are seeing is a single case being infected, then going back to a household and all that household becoming infected.”

He said that as a result the borough was limiting the number of other people residents can visit, requiring face masks to be work in public places and sending mobile testing units out into the community.

Harrison said that if infection numbers did not fall by July 27, officials would begin to reimpose lockdown measures such as the closing of shops and other businesses.

Harrison said he hoped Blackburn would not have to impose a blanket local lockdown like one in the city of Leicester. The government ordered restaurants, pubs and non-essential shops to close there on June 30 after the infection rate surged to 157 cases per 100,000 residents.

Health Secretary Matt Hancock said the government would assess Leicester’s lockdown on Thursday when the latest coronavirus data is out. He said the number of infections in the city was falling but remained “well above the rest of the country.”

Like Blackburn, Leicester has a large South Asian population. Statistics show that Britain’s ethnic minorities are more likely to contract the virus than their white counterparts. Experts point to a range of factors, including social inequality and the prevalence of underlying health conditions such as diabetes.