My 17 yo daughter ate one bite of very old canned tuna from grandfathers house. she spit out some but did swallow small amount. chance of illness?

Slim: Canned food is typically quite safe even when beyond expiration. If the can was not swollen, punctured, or rusted through, it was likely still preserved. However if gastrointestinal symptoms develop, be sure and let your treating physician know about the tuna.

Food poisoning: Food poisoning onset is usually within hours except in the case of fecal contaminants like e.Coli or campylobacter. You'll know soon, but the chance is small.