Construction crews working at a Perth factory which builds components for Covid-testing kits have had to down tools after a surge in coronavirus cases.
An emergency taskforce has been set up to monitor the outbreak at the Thermo Fisher Scientific plant.
The number of staff who have tested positive at Auld Bond Road facility has more than trebled, from six to 22 in just under a week.
A section of the site, which is under construction as part of a business expansion, has now been closed for a deep clean.
The decision to shut off the area was taken by contractors Robertson Construction who said its staff should be able to return on Friday, but only if they test negative.
The closure does not affect production in the main part of the building, which remains operational.
The factory plays a crucial role in the international fight against the pandemic. Since October, Thermo Fisher has been manufacturing crucial pieces for Covid-19 tests.
About eight million tubes are created at the factory each week. They ensure that samples collected from nose swabs maintain their viability while they are sent away for testing.
A spokesman for Thermo Fisher confirmed that 22 staff linked to the factory had now tested positive.
He said safety, health and well-being of colleagues was the firm’s top priority.
“We remain in close contact with local health authorities and are following all required protocols to ensure the continued health and safety of our employees,” he said. “A wide range of control measures are in place across the site and we continue to regularly review our protocols to maintain a Covid-19 safe environment.
A spokeswoman for Robertson added: “Following confirmation of a positive test result within the workforce, the construction site closed immediately and a deep clean was instructed.
“While the site has remained closed, all members of the workforce were encouraged to be tested.”
She said: “We have been made aware of further positive test results and as a precaution kept the site closed whilst we undertake internal investigations and a deep clean in line with our Covie-19 safe operating procedures.”
The spokeswoman, who also said that safety was a priority, added: “Following a thorough inspection by our health and safety team the site will re-open on Friday to those who have returned a negative test result.”
It is understood the construction site is not used by Thermo Fisher employees.
An Incident Management Team (IMT) – a partnership of health experts and local officials set up to control and investigate the situation – met on Thursday morning to review the cluster.
An NHS Tayside spokeswoman said: “NHS Tayside’s Health Protection Team has been made aware of 22 cases of Covid-19 connected to Thermo Fisher Scientific factory.
“The factory is working closely with NHS Tayside’s public health team and Perth and Kinross Council. Contact tracing is complete and staff are being given appropriate advice and support to self-isolate if required.”
She said that there are no plans for the IMT to meet again, adding that the public health team will “keep the situation under close review”.
The US-based company last year announced an expansion of the Auld Bond Road plant as part of a $140 million (approximately £100m) investment, creating 200 jobs.
The firm said it was growing its laboratory plastics disposables production to meet global demand for Covid-19 testing.