Stool comes out of fistula wound. Right?

I had surgery last weekend to remove fistula but it was so deep that the doctor had to opt for thread treatment where they had tied a thread from a fistula opening to anal canal. Pain has decreased after the procedure and I have been told that this thread needs to be changed every week. Now, the problem is that while passing the stool, some of the stool comes out of the fistula opening and i had to clean it until it's fully discharged which takes at least 2-3 hours after I pass the stool in the morning. Is this normal? Will this not cause infection? Even though I try to keep the wound clean, the stool in the fistula canal can definitely cause an infection, right? How to deal with this situation as my doctor says that it's normal and all I need to take care of is hygiene.