Does a small bleeding tear inside anus when pooping constipated stool increase chance of catching disease from using public toilet (e.g. water splash?

I'm not sure...: ... that this specific problem has ever been studied in detail. However, any open wound is susceptible to infection, and certainly there are a lot of bacteria present both in that area of the body and in public toilets. If I had a perianal tear, I would try to avoid water splashing on it. You should see your doctor if the bleeding or pain are persistent . Good luck.