Dell's approach is much more elegant and moves the processing onto the server but if you cannot get it to work you should be able to do this through group selectin criteria.
Keep in mind that group selction criteria happens after summarizations so if you are doing any counts or summary of the data you need to do that with runningtotals or shared variables that also exclude the groups.
group on visit number
create a 'flag' formula
//is_99211
If table.CPT ="99211" then 1
insert a count of the cpt code field at the vistinumber group
do a sum of of the formula field at the visitnumber group
now you can use the two values for your condition
Count(cpt,vistinumber)<>sum(is_99211,visitnumber)