Coronavirus was likely being spread across Scotland at a community level in February - the month before lockdown restrictions were implemented, it has been revealed.
Dr Gregor Smith, the country's chief medical officer, said experts had recently analysed strains of Covid-19 found in the early weeks of the outbreak.
While most of them are believed to have originated from abroad, some had not.
"Not all of them have a travel history - what that suggests is there was some form of community transmission underway in Scotland - probably in February," Dr Smith said at the Scottish Government's daily media briefing.
But the health expert added: "While it's fair to speculate that there were a few cases (in February) there's no evidence of widespread transmission."
Nicola Sturgeon said there was no evidence she had seen to suggest a spike in deaths the month before lockdown.
The first recorded case of Covid-19 in Scotland not thought to have been contracted from overseas was on March 11, while full lockdown across the UK was not implemented until the evening of Monday, March 23.
Dr Smith added the "lineages" found in Scotland were mainly associated with the continental European epicentre of the virus.
He said the research "has identified viral lineages with no clear link to travel at the very early stages of the outbreak in Scotland, suggesting that there may have been earlier introduction to Scotland, and community spread, even before the first cases emerged".
Discussing the outbreak associated with the Nike conference, which led to eight Scottish cases of coronavirus, he said direct evidence of further spread had not been established.
Dr Smith said: "This particular sub-lineage of the virus has not been detected in Scotland since towards the end of March.
"This suggests that the actions taken by the IMT (incident management team) to manage this outbreak were successful in curtailing spread and led to the eradication of this particular viral lineage."
He stressed the number of cases in February would have been very small, with the main peak taking place towards the end of March and early April.
