After you eat a contaminated food, there is an hours-to-days delay before you notice symptoms. The contaminating organism passes through the stomach into the intestine, attaches to the intestinal walls, and begins to multiply. Some organisms stay in the intestine. Some produce a toxin that is absorbed into the bloodstream. And others directly invade body tissues. Your symptoms depend greatly on the type of organism that has infected you.
Different organisms cause similar symptoms, especially diarrhea, vomiting, and stomach cramps. Diarrhea and vomiting are a normal response as the body tries to rid itself of harmful organisms. Unless the illness is part of a recognized outbreak, it's difficult to identify the infecting organism. Lab tests usually aren't done.
In most cases, you recover in a few days to a week as toxins are flushed from your system. You may feel weak for several days after other symptoms go away.
Most of the time, food poisoning is mild and passes in a few days. But the symptoms and course of some types of food poisoning may be more severe. To learn more, see Symptoms for a list of specific organisms.