When I was in college I had a full time job at Walmart. At the time, Walmart did not pay you for the first day off sick (even though we had 40 hours of sick time each year). They would pay you for the second day off sick, but only if you had a doctor's note.
Of course, I couldn't afford a doctor and couldn't afford a day off from work unpaid. So I didn't take sick time unless I was dying.
I don't think I was ever healthy at that job. People would just work while they were sick, for the same reasons I did.