Yikes, talk about digging in Pandora’s Box! Can 500 year old medical waste still be infectious after having been buried that long? I sure wouldn’t want to find out.
There are some bugs that can persist in the soil (which is probably where they originated) for very long periods of time. Typhus has been around as a documented problem since the 16th century, and is likely the (or a) culprit in the pestilence that ravaged ancient Athens during the siege by Sparta. Decades ago I read of at least one case of typhus caught from an archaeological dig of a site buried for over 10,000 years, but in that case, who really knows if it wasn’t contracted in one of the normal ways.
Smallpox and plague can last indefinitely