A total of ten people have now been admitted to hospital with the new variant.
Some 21,975 confirmed, probable and possible Omicron cases were recorded as of December 19.
Of these, just 1,111 have been confirmed by genomic sequencing, which can take weeks to process.
But S Gene dropout, a very likely indicator of Omicron that shows up in PCR tests, has been recorded in 20,777 cases.
A further 87 Covid cases are thought to possibly be of the new variant.
It is believed to be significantly more transmissible than previous variants, with an R number well above three.
The highest number of Omicron cases have been recorded in the largest health board, Greater Glasgow and Clyde, at 6,532 cases.
There have been 5,756 cases recorded in NHS Lothian, and 3,358 in Lanarkshire.
All health boards have recorded cases of Omicron, including five probably cases in Shetland, ten in Orkney and 12 in the Western Isles.
Scotland has seen a rapid increase in Covid-19 testing, PHS said, with lateral flow tests up 67 per cent since last week.
Almost 829,000 lateral flow tests were recorded in the week to December 20, with 8,548 positive results.
A total of 2,434 new Covid cases were reported on Wednesday, a significant drop on the figure of over 5,000 the day before. PHS said it is investigating the unexpected decrease.
Members of the public have been urged to take lateral flow tests before attending events or socialising, especially over the Christmas period.
“Please follow advice to keep family celebrations as safe as possible,” Ms Sturgeon said on Tuesday.
"Keep gatherings as small as family circumstances allow. Make sure everyone does a test shortly before getting together.
" Anyone who tests positive should not mix with others. And given how infectious Omicron is, you should assume that if one member of a household is positive, the others are likely to be so too.”