Thanks for the query.
He might have developed bacterial infection.
That is the reason for pus
Treatment is with antibiotics but the choice of antibiotics should be based on culture and sensitivity tests.
Its good that they have taken pus for culture.
Just maintain good hygiene and wait for culture report.
It will help in finding out the exact cause.
If possible surgical drainage
can also be done.
Please meet a dermatologist
for exact diagnosis.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.