American Medical Association Family Medical Guide - American Medical Association [510]
Infections of the Digestive Tract
The intestines normally contain harmless bacteria; some bacteria that inhabit the intestines have beneficial functions such as manufacturing vitamins. An infection of the digestive tract occurs when infectious agents, such as viruses or bacteria, multiply rapidly in the stomach or intestines. The presence of microorganisms in the digestive tract is not considered an infection unless the microorganisms exist in large numbers and cause symptoms.
Gastroenteritis
Gastroenteritis is a general term that refers to irritation and inflammation of the digestive tract, especially the stomach and intestines. It is most often caused by a viral infection that spreads easily from person to person—even without having direct contact or consuming contaminated food or water. Viral infections are the most common cause of the 24- to 48-hour attacks of vomiting and diarrhea that are commonly called stomach or intestinal flu.
Eating or drinking contaminated food or water (food poisoning; see page 783) can also cause gastroenteritis. Gastroenteritis that occurs after eating something that contains a toxic substance, such as a nonedible mushroom or a rhubarb leaf, is not actually food poisoning but can cause a severe attack. Eggs, milk products, and shellfish can cause allergic reactions in people who are sensitive to those foods (see page 915).
Another possible cause of gastroenteritis is a change in the population of bacteria that normally live in the digestive tract. If you have an illness that weakens your immune system, or if you suddenly make changes in your diet (such as when visiting another country), the balance of bacteria in your digestive tract can become disturbed. When some strains of bacteria become stronger and multiply at the expense of others, the result can be an upset stomach and irritated intestines. Antibiotic drugs also can disturb the bacterial equilibrium in the intestines, permitting unchecked growth of bacteria that can lead to infections such as the common yeast infection candidiasis (see page 880).
The severity of an attack of gastroenteritis depends on the type of infectious agent, the number of infectious microbes, the amount of contaminated food substances you have eaten, and your age and general health. The risk of serious illness is greatest for newborns, children younger than 18 months, and older people who are chronically ill or who have a weakened immune system. In a healthy person, an episode of vomiting and diarrhea is rarely serious. But persistent diarrhea can cause dehydration and loss of essential body salts, which upsets body chemistry and, if not treated, can lead to shock (see page 579). Severe and persistent pain in the abdomen (not just an occasional cramp) can be a sign of a more serious abdominal disorder.
Symptoms
The symptoms of gastroenteritis range from a mild attack of nausea followed by diarrhea to a severe illness. You may have only one or two bouts of vomiting and soft stool, or you may vomit repeatedly and have recurring attacks of watery diarrhea with abdominal pain and cramps, fever, and extreme weakness. Occasionally, a severe case of gastroenteritis lasts so long that it is disabling. In most cases, however, the symptoms go away within 24 to 48 hours. If your symptoms last for 5 days or more, if you notice any blood in your stool, or if you have symptoms of dehydration (such as light-headedness, a rapid pulse, and little urine output), see your doctor right away.
Diagnosis
If you have symptoms of gastroenteritis, your doctor will perform a physical examination and may take a stool sample for laboratory evaluation. The doctor will ask you questions about what you have eaten and whether any family members or other people you have come into contact with are also ill. He or she may know about a local epidemic of gastroenteritis and its cause, which will help determine treatment.
Treatment
Because most attacks of gastroenteritis clear up on their own, you can perform self-help measures at home to keep you from