Signs and Symptoms:
Gastrointestinal (GI) infections usually cause diarrhea - frequent and watery bowel movements. Viruses, bacteria, or parasites can all cause diarrheal infections, which means that a child can exhibit a variety of symptoms. Symptoms usually start with crampy, abdominal pain followed by diarrhea. This usually lasts a few days but can last longer in some cases.

When GI upset and diarrhea last more than 2 weeks, the condition is known as chronic diarrhea. Some infants with chronic diarrhea either fail to grow (known as "failure to thrive") or begin to lose weight, but otherwise may not show any other symptoms of being ill. However, excessive loss of water, especially with explosive, frequent episodes of diarrhea, can lead to severe dehydration, especially in small children.

Blood may also be found in a child's diarrheal stools, which indicates that the infectious germ is causing damage to the lining of the bowel. This is seen more often in certain bacterial infections caused by Campylobacter jejuni, Salmonella, certain strains of Escherichia coli (E. coli), and Shigella, in which case the stool may contain mucus as well as blood.

Nonbloody diarrhea is usually caused by infections with other bacteria, viruses, or parasites or by ingestion of a toxin (poison) produced by bacteria. A common viral intestinal infection is rotavirus, which usually causes explosive, watery diarrhea.

Many of the viruses, bacteria, and parasites that cause diarrhea also cause other symptoms, such as fever, loss of appetite, abdominal cramps, nausea, vomiting, weight loss, and dehydration.

Occasionally the germs that cause diarrheal infections may spread into the bloodstream and cause infections in organs far from the intestines. Salmonella bacteria, for example, can cause infections in the bones (osteomyelitis), joints (arthritis), brain (brain abscess), membranes covering the brain (meningitis), and elsewhere. This is especially true for children with chronic illnesses involving the spleen, such as sickle cell disease.

Description:
The specific germs that cause diarrhea often depend on the geographic area and its level of sanitation, economic development, and hygiene. For example, countries with poor sanitation or where human waste is used as fertilizer tend to have outbreaks of diarrhea when intestinal bacteria or parasites (such as ascariasis) contaminate crops or drinking water. In developed countries, including the United States, outbreaks of diarrhea are more often linked to contaminated water supplies, improperly processed or preserved foods, or person-to-person contact in places such as child care centers.

A common viral cause of diarrhea in American children is rotavirus. Almost all children who live in the United States have had a rotavirus infection by the time they are 4 or 5 years old, although not all children show symptoms. The viruses can live for significant periods of time on toys and surfaces in play areas. Rotavirus commonly causes outbreaks of diarrhea during the winter and early spring months, especially in child care centers and children's hospitals. Hand washing in these places is very important to stop the rapid spread of outbreaks of rotavirus.

Another viral infection that causes diarrhea in children, especially during the summer months, is from enteroviruses, particularly group A and B coxsackie viruses.

At least 13 different types of bacteria can cause diarrheal infections, including Salmonella, Shigella, E. coli, and Campylobacter. In the United States, Salmonella bacteria cause between 1 and 5 million cases of diarrheal illness each year and are responsible for over 50% of the nation's food poisonings.

Shigella bacteria, which commonly spread from person to person, infect 140 million people around the world annually and are especially dangerous because they attack the intestinal wall and cause ulcers that bleed. As few as ten Shigella bacteria are enough to cause an infection, so Shigella infection (shigellosis) spreads easily in families, hospitals, and child care centers.

Five different classes of E. coli cause diarrheal infection in children, most often during their first few years of life. E. coli bacteria can cause diarrheal illness by either directly attacking the intestinal wall or by producing a toxin that irritates the intestines. One of the most dangerous E. coli infections is E. coli O157:H7, which produces a toxin that can lead to hemolytic uremic syndrome - a severe illness that can seriously damage many organs, including the kidneys, and cause intestinal bleeding. Most E. coli infections are spread through contaminated food or water. Undercooked beef in hamburgers can be a source of E. coli infection.

Parasitic infections associated with gastrointestinal symptoms in the United States are most commonly caused by Giardia, which is easily spread through contaminated water supplies and human contact. This parasite can be spread in water parks and pools because it's resistant to chlorine treatment. It can also be transmitted through children's "touch tanks" in aquariums and museums. Bathing in and drinking water from contaminated streams or lakes can also lead to infection (so be careful when you go camping!). Giardia infection can cause chronic diarrhea and malabsorption of food.

Cryptosporidium, another parasitic organism, is also a frequent cause of gastrointestinal illness in children. It's commonly involved in diarrhea epidemics in child care centers.

Prevention:
Hand washing is the most effective means of preventing diarrheal infections that are passed from person to person. Dirty hands carry infectious germs into the body when a child bites his nails or puts any part of his hands into his mouth. Children should wash their hands frequently, especially after using the toilet and before eating.

Clean bathroom surfaces also help prevent the spread of infectious germs.

Food and water also can carry infectious germs, so be sure to wash fruits and vegetables thoroughly before eating. Wash kitchen counters and cooking utensils thoroughly after they have been in contact with raw meat, especially poultry. Refrigerate meats as soon as possible after bringing them home from the supermarket, and cook them until they are no longer pink. After meals, refrigerate cooked leftovers as soon as possible.

When traveling, never drink from streams, springs, or lakes unless local health authorities have certified that the water is safe for drinking. In some developing countries, it may be safer to drink only bottled water and drinks rather than water from a tap. Also, exercise caution when buying prepared foods from street vendors, especially if no local health agency oversees their operations.

Pets, especially reptiles, can spread germs if their feeding areas are not separate from family eating areas. Never wash pet cages or bowls in the same sink that you use to prepare family meals.

Incubation:
Incubation times vary depending on the germ causing the infection. For example, the Shigella incubation period is usually 16 to 72 hours, but viral incubation periods can run from 4 to 48 hours. Parasitic infections generally have longer incubation periods, such as a Giardia infection, which has an incubation period of 1 to 3 weeks.

Duration:
This also varies depending on the germ and the child. In cases of mild diarrhea caused by a virus, the diarrhea passes after a few days and the child recovers completely with supportive care, rest, and plenty of fluids. For most diarrheal illnesses caused by bacteria and viruses, antibiotics or antiviral medications are not used because most children recover on their own. In very young children or in children with weak immune systems, antibiotics are sometimes given to prevent a bacterial infection (such as salmonellosis) from spreading through the body. Most parasitic infections are treated with antiparasitic medicines to cure or shorten the course of the illness.

Contagiousness:
Diarrheal infections are contagious. They can spread from person to person via dirty hands, direct contact with fecal matter, contaminated food or water, and some pets. Again, frequent hand washing is one of the best ways to prevent the spread of infection.

When to Call Your Child's Doctor:
Call your child's doctor whenever your child has a severe or prolonged episode of diarrhea, fever, vomiting, or severe abdominal pain or if the diarrheal stools contain blood or mucus.

Call your child's doctor immediately if your child seems to be dehydrated. Signs of dehydration include dry lips and tongue, skin that is pale and dry, sunken eyes, listlessness or decreased activity, and decreased urination (such as fewer than six wet diapers a day in an infant).

Professional Treatment:
The immediate goal of treatment of all diarrheal illnesses is to maintain adequate fluid intake with appropriate rehydrating solutions. These can be taken by mouth or given into a vein if the child is severely dehydrated. Infants and small children should never be rehydrated with water alone because it does not contain adequate amounts of sodium, potassium, and other important nutrients.

Your child's doctor may take a sample of your child's bowel movement to be tested in the laboratory to identify the germ directly. If your child's illness is caused by a parasite, it can be treated with antiparasitic medicines. Diarrheal infections caused by viruses and most bacteria are not usually treated with medicines because most children recover on their own.

Home Treatment:
The primary concern when treating a diarrheal infection is the replacement of fluids and electrolytes (salt and minerals) lost in diarrhea, vomiting, and fever. Depending on the amount of fluid loss and the severity of vomiting and diarrhea, your child's doctor may ask you to switch your child to a milder diet for 1 or 2 days, use special drinks to replace body fluids quickly, or simply give your child more liquids.

Copied from:   http://kidshealth.org/parent/medical/digestive/gastrointestinal.html