In fact, unless the burger meat was kept at room temperature for a while, it was most likely not the burger at all. Staphylococcus aureus food poisoning is due to the enterotoxin secreted by the bacteria, not the bacteria itself. The enterotoxin comes from bacteria that have been allowed to multiply in food left unrefrigerated for a period of time. Ground beef is usually refrigerated or even frozen until it's time to use it, so no enterotoxin would have developed in your medium-rare burger unless through cross-contamination (i.e. the beef handler touched something or was already sick himself before handling the beef). But plenty of other foods are just as or more likely to be affected by cross-contamination and it's not likely the beef remained unrefrigerated long enough for sufficient enterotoxin to develop.
Also, because it's a toxin and not a bacterial infection that is making you ill, treatment is usually just to let the disease runs its course, not to prescribe antibiotics unless it's a potentially fatal case of acute enteritis that may occur in the elderly. I stand by my earlier assertion that Cipro, no matter who prescribed it, was swatting a fly with an AK-47 and over-prescription of unnecessary antibiotics puts the rest of us in danger.
To avoid possible risk factors, it's best not to eat food at all. You basically never know when cross-contamination will get you. But go ahead and eat those medium-rare burgers as they're likely safe.
