Any wound or burn has a chance of becoming infected. The wounded character makes an Infection Roll target difficulty Mediocre(-1) modified by the care they receive.
Untreated: No modifier
Treatment within 8 hours by someone with the Medicine skill: +1
Treated within 8 hours by someone with the Medicine skill and antibiotics: +2
Mitch gets shot while foraging for supplies. He makes it back to camp and The Padre takes a look at it, though he's out of antibiotics. Mitch then makes a roll at +1, so as long as he gets a Poor/-2 or better on the dice he doesn't get an infection\
Effects of Infection
Infected characters cannot heal damage.
A medicine check can be made each week vs. Average diffculty to cure the infection.