Medical bills are usually not reported to the credit bureaus unless they have been unpaid for a long time and have gone to collections. Collections accounts stay on the report for as long as seven years even after you’ve paid them off. These accounts typically hurt scores, though some scoring models do not include medical collections, especially those with small balances of less than $100. VantageScore^® 3.0 does not take paid collections accounts into account in its model.

Source: https://www.vantagescore.com/press_releases/how-to-deal-with-medical-bills-on-your-credit-report/