Physical Danger
Germs, diseases, needles, experimental drugs, and thin latex gloves...what could go wrong? Regardless of the job, you'll be surrounded by stuff that can get you sick or kill you. Take precautions, take care, and take vitamins—seriously. Don't let your concern for others get in the way of concern for yourself. Your immune system isn't in better shape just because you've studied this stuff.
Stress and lack of sleep will also lower your defenses, so be sure to get rest, maybe do some yoga, and generally live a healthy life. And wash your hands. A lot.