A record 6,757 alerts were sent through the app in the seven days to July 7, raising fears of a lockdown by stealth as businesses and transport being brought to a standstill by a ‘pingdemic’ next week.
The city saw a rise of more than a third compared to the previous week’s figure of 4,991, and was the seventh highest figure in the country.
There have been claims by some that they had been pinged without leaving their homes, with some suggested signals had passed through walls.
Dr Fiona Sampson, a senior research fellow in emergency and urgent care at the University of Sheffield said her partner got an alert – despite not leaving the house on the day of the contact.
She said: ‘We later realised he had been working with his phone on the table, less than two metres away from our neighbour.’
Employers have warned of a looming staffing crisis.
Rail, Maritime and Transport union (RMT) general secretary Mick Lynch warned Monday "will see a surge in workers pinged with a self-isolation instruction next week".
"Even at this late stage, the Government, the train operators and the bus companies should issue a clear, legally backed instruction that levels up the rest of the UK to the safety standards that will remain in force in Wales and Scotland," he added.
But a spokesman for Stagecoach South Yorkshire said their services had not been significantly impacted by the current situation with the increase in coronavirus cases and people having to self-isolate across the country.
They said: “The flexible and supportive approach of our drivers and the hard work of our control teams behind the scenes means that we have managed to continue running almost all of our journeys.
“Most schools are closing in Sheffield this weekend for the six weeks of school summer holidays. This is helpful for us as we need slightly fewer staff with no school buses during this period. ”
Pubs and restaurants were also issuing warnings over possibly having to close their doors due to the level of pings.
UKHospitality chief executive Kate Nichols said the industry is facing "significant staffing challenges".
Fully-vaccinated individuals will be exempt from having to quarantine over close contacts, but the change will not be introduced until August 16.
A spokesman for 10 Downing Street said: "We keep things under review but the app is doing what it is designed to do," a No 10 spokesman said.
The spokesman also sought to alleviate concerns that people were being asked to self-isolate because they have been pinged through the walls of their house, but could not rule it out.
"We're confident that that is not contributing to large numbers of individuals being asked to self-isolate," he said
"The app uses low-energy Bluetooth and its signal strength is significantly reduced through things like brick walls, so therefore it is highly unlikely that through brick walls would lead to an alert."