More than 3,500 Scots who have tested positive for Covid-19 have not been spoken to by coronavirus contact tracers.
In addition, more than 9,000 people who were contacts of someone with the disease were unable to be traced.
The figures were made public at the same time as it was revealed a “coding error” was found to be responsible for overestimating the number of people contacted within 24 hours of testing positive for the virus.
Now the Scottish Government has said there are a “small minority of cases it has not been possible to reach”.
It said these individuals have not responded to “repeated attempts by the contact tracing service”.
Public Health Scotland figures show that since June 22 a total of 3,512 individuals with a positive test were unable to be contacted by staff from the Test and Protect system.
The report said this was 6% of those who had tested positive, describing it as a “very small proportion” of the number of cases.
There were a further 9,252 contacts of coronavirus patients were unable to be reached since June 22 – representing 4% of this group.
Labour health spokeswoman Monica Lennon said: “Thousands of people who tested positive have slipped through the net, as have thousands of their close contacts.”
She called for action from both First Minister Nicola Sturgeon and Health Secretary Jeane Freeman.
Ms Lennon added: “The Cabinet Secretary and the First Minister need to cut out the spin and complacency.
“Fix Test and Protect for all our sakes.”
A Scottish Government spokeswoman said: “It is vital people engage with contact tracing teams whether they have been tested for Covid-19 or are identified as a contact.
“Anyone taking a test will be asked to provide their name and a contact phone number.
“Contact tracers will call and text this number three times over 24 hours and, if not reached, a message is left to call the contact tracing service back.
“In a small minority of cases it has not been possible to reach individuals who do not respond, despite repeated attempts by the contact tracing service.”
The spokeswoman added: “Our contact tracers have successfully interviewed 94% of people who have tested positive for coronavirus.
“In the week from November 2 to November 8, Test and Protect completed 95.8% of cases within 72 hours – far exceeding the World Health Organisation standard of 80%.”
The most recent figures for England show that between October 22 and October 28 contact tracers were unable to reach 20,846 people who had tested positive and were transferred to the contact tracing system.