How to count each value of a variable as separately that is tied to a singular event

[jasmineburbank]

Hello,

In my dataset each person (eventID) is associated with 1-3 pathogens (pathogenSeq). I want to look at the total counts of each of the pathogens, but some people have tested with more than 1 pathogen. How would I make it so that if a person has multiple pathogens they are counted for each pathogen? 

Here is what I tried per my teacher's advice but the output is blank: 

proc sort data=infection;
by eventID pathogenSeq; run;

data infection2;
set infection;
if first.pathogenSeq = 1 then count = 0;
count = count + 1;
if last.pathogenSeq = 1 then output;
retain count; run;

Would it make more sense to create a new variable for pathogen? Any help is appreciated, thanks!

[Astounding]

To get started, insert the missing statement. Following the SET statement, repeat the BY statement exactly as it appears in the PROC SORT step.

[jasmineburbank]

I added a BY statement and did not receive any error messages.

How would you recommend I verify the procedure worked properly?

[andreas_lds]

Maybe:

proc summary data=have nway;
  class pathogenSeq;
  output out=counted(drop= _type_ rename=(_freq_ = count));
run;

If this doesn't work, please post example data in usable form together with the expected result.