I'm reaching the end of my knowledge, but I would guess that there's a good tradeoff between reducing the number down to 2% vs culling down to the "best" remain

I'm reaching the end of my knowledge, but I would guess that there's a good tradeoff between reducing the number down to 2% vs culling down to the "best" remainder. You also give your immune system more time to catch up and take car of the rest for you. If you can, with antibiotics, kill off 98% and prevent growth over a week, you immune system can probably handle the rest and you transfer 0 to the next person.