Karen Cole-Peralta published an article at the American Chronicle Web site titled, "Food Poisoning – An Overview,".  She wrote about common causes of food poisoning, including Campylobacter jejuni, E. coli O157:H7, and Clostridium Botulinum (botulism).  Here is an excerpt from the article:

Over 55% of such cases are caused by improper cooking and storage of foods, and 24% by poor hygiene, such as not washing your hands while preparing food. Only 3% of cases are from unsafe food sources. Keeping your hands clean while working with food is the single most important thing you can do to prevent food poisoning.

About 20 organisms can cause food poisoning. After you eat food contaminated with bacteria, they will multiply in your stomach and bowels. Some bacteria give off a toxin when they multiply. As a result, nausea, vomiting, abdominal cramps and diarrhea occur. Vomiting and diarrhea are the body’s way of eliminating the toxin, and most cases of food poisoning run their course without needing medical attention.

Not all invasive organisms cause vomiting as a symptom, but almost all of them cause diarrhea. Blood in your stool occurs in many types of food poisoning and is considered to be serious. Abdominal cramps are also common, and sometimes you will have a fever. Be sure to contact a physician if a fever or bloody stools are present.