I'm fortunate to work somewhere with very generous leave benefits, but it wasn't always so. 20 years ago I managed a coffee shop while the owners went to LA to become movie stars. I was put on salary, and before they left they made me sign something saying that if I was sick and needed someone else to cover my shift, the wages would come out of my paycheck. I signed it, because I rarely get sick. Wouldn't you know it - I got the sickest I'd been in about 12 years. Bronchitis. And I worked every single shift of my food-service job, because I had no insurance, made $7.50 an hour and couldn't afford to have my paycheck docked. The owners did feel bad when they heard how sick I was and they paid the bill for my doctor visit, but they didn't take back the clause about docking my salary if someone else had to work for me (which I'm pretty sure is illegal, but I didn't know that then).
I can still remember willing myself not to cough when customers were in the shop, and then going and hacking up a lung the second they left. I washed my hands A LOT during that time