First, it should be noted that answers on eNotes exist only for the purpose of academic study and are not intended as medical advice. If you are interested in obtaining medical advice, you should consult your health care provider.
Food poisoning is defined as a form of illness resulting from ingestion of contaminated food, whether the contamination is by bacteria or other toxins. There are actually several hundred types of infection or reaction that are categorized under the rubric of food poisoning.
Typical symptoms begin between two and eight hours after consuming contaminated food and include stomach distress (cramps, nausea, diarrhoea, vomiting) and sometimes sweating.
Gastroenteritis, the affliction popularly called "stomach flu" is caused by inflammation of the stomach or the intestines. Since this can be a result of bacteria or viruses consumed in food, the two are not always distinct. Symptoms always include diarrhoea and may also include vomiting and fever. Fever can be used to suggest the diagnosis of gastroenteritis, but an accurate diagnosis can only be obtained by a stool culture.
As abdominal distress may be a symptom of other more serious conditions, patients suffering from severe or prolonged symptoms should consult their healthcare providers for appropriate tests and diagnosis.