So I've done some google searches on whether there is any way to treat colonists medically when they're on their own and I haven't found anything. I've seen a few suggestions that colonists should be able to treat themselves from quite a while back, but if that's maybe bad for balancing or AI reasons, I have a different suggestion. Maybe with the new alpha 16 features, you could form a caravan and send them off to seek medical treatment from a nearby faction base. It would maybe cost an amount of silver based on the severity of the wounds/infections (at point of arrival) and would force your colonist to remain in caravan until they were healed (which they would do normally and any infected wounds would progress at the normal well-treated rate). This would also help people who have nobody capable of doctoring, but also would take too long to allow people who are critically wounded to just treat themselves in the absence of a doctor. It's more for those times when you don't have a doctor and don't want the fact that you were attacked by a crazy hare to be a death sentence.