There's no provision to exclude OU's in a filter (or to include them, either), but you can exclude them from the results.
$Syntax = "(co -like '*USA*')"
Get-ADUser -Filter $Syntax -Properties DisplayName,SamAccountName,EmailAddress,Userprincipalname |
Where-Object {$_.distinguishedName -notlike "*,OU=TempOU,OU=MYOU,DC=*"} |
Select-Object DisplayName,SamAccountName,EmailAddress,Userprincipalname|
Export-csv C:\temp\output.csv -Notypeinformation