One option you can do is to continue with your replacing of the string without the comma. Then follow that replace with another replace and check if the remaining string starts with a comma and if it does, then remove that extra comma. If the text that was replaced is in the middle of the selection, then look for two consecutive commas and replace it with a single comma.
So for case #1, "<strong>Cough</strong>,Cold" becomes ",Cold". Since it starts with a comma, replace that first comma with an empty string.
And for case #2, "Flu,<strong>Cough</strong>,Cold" becomes "Flu,,Cold". Since there's 2 commas together, replace that with a single-comma.
Hope this helps.
Regards,
SQL Server Helper