A rise in confirmed coronavirus cases in Swindon is largely due to a mini outbreak at the Iceland distribution centre, according to local leaders.
Health bosses from Swindon Borough Council said a mobile testing centre at XPO Logistics has picked up on those who are asymptomatic - causing a spike in the number of cases in the town.
Rate of new Covid-19 cases per 100,000 people in Swindon, in the seven days up to 31 July.
Rate of Covid-19 cases per 100,000 people in the town, in the seven days previous.
In the week leading up to the end of July, Swindon's increase in coronavirus cases was the largest rise per 100,000 people in England.
According to PHE, there were 108 new cases during those seven days, compared to 44 in the week ending 24 July.
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Swindon Borough Council's cabinet member for adults and health said the majority of the new cases were at the town's Iceland depot.
Brian Ford told the PA news agency that mobile testing teams at the site, brought in because of the outbreak, were picking up on asymptomatic cases.
This, he said, is fuelling the growing numbers in Swindon.
Mr Ford said, "The cases are rising through one specific incident with a firm called XPO, they have a workforce of approximately 700 and we have mobile testing teams in there."
The rising cases is because we are picking up with that testing a lot of asymptomatic cases, normally they would not be found. Whilst we have a couple of other tiny little outbreaks, ones and twos, this is the main one.
The mobile testing unit at XPO's Penzance Drive distribution centre has been there since Wednesday 29 July. 457 members of staff were tested in the three days following its arrival, the company said.
Mr Ford said he hopes the outbreak will be over in a week and added, "In fairness, the company is doing everything it is being asked to do.
"We would hope the figures all start to decrease as the week goes on."
XPO Logistics has been approached by PA for comment.