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Food poisoning is generally caused by the ingestion of food which is contaminated with certain species of bacteria. Contamination with viruses, parasites, and certain chemicals can also cause food poisoning. The symptoms of food poisoning differ somewhat depending on the cause, but most cases of food poisoning include symptoms such as vomiting, diarrhea, and stomach cramping.
In addition to these three common symptoms, there are a range of other symptoms of food poisoning which may be present depending on the infecting organism. Diarrhea disease caused by bacterial infection tends to also cause fever, and may also result in the appearance of blood or mucus in stools. Food poisoning caused by viral infections, on the other hand, often causes headaches and vomiting.
In general, diarrhea is more likely to be caused by a bacterial infection, while vomiting is usually caused by a viral infection. There are some exceptions to this rule, however. Some illnesses, such as cholera, cause severe vomiting and diarrhea. Other microorganisms cause a more unique range of symptoms that are not limited to the gastrointestinal tract. One such case is that of botulism, caused by the bacteria Clostridium botulinum. Symptoms of botulism include paralysis of skeletal muscle as well as nausea and vomiting.
Signs of food poisoning are associated with the development of inflammation in the gastrointestinal tract. Growth of bacteria, viruses, or parasites, secretion of toxins by microorganisms, and the presence of certain chemicals, can cause this kind of inflammation. The inflammation and excess water loss is the result of damage done to the intestinal wall by toxins secreted by microorganisms, by the microorganisms themselves, or by ingested chemicals.
Many people with food poisoning also experience symptoms of dehydration. This is because large amounts of fluids can be lost as a result of vomiting or diarrhea. Dehydration can cause nausea, fatigue, and dizziness. Urine appears darker in color, the mouth and nose may feel dry, and cramping may occur in the limbs. To combat dehydration, people with food poisoning should drink plenty of liquids, but should drink slowly without ingesting large amounts of fluids at any time.
Symptoms of food poisoning may be of sudden onset, or of delayed onset. Symptoms of salmonella food poisoning, for example, usually appear within one to three days of ingestion of contaminated food. In contrast, ingesting food contaminated by Staphylococcus aureus causes symptoms of food poisoning within six hours. Parasites such as Giardia intestinalis, and the bacteria Listeria monocytogenes, have an incubation of period of up to four weeks before they begin causing symptoms.