Dr. Reddy's Pediatric Office on the Web TM


Almost everyone has had, or will have, what many people call stomach flu. Doctors call this "gastroenteritis", which means irritation of the stomach and the intestines. Although it often goes away by itself in a couple of days (thus the term "24-hour flu"), it sometimes lasts longer -- and having it is miserable for everyone concerned.

The symptoms can vary depending on the cause of the illness, but the "classic" signs of stomach flu are a combination of diarrhea, fever, and vomiting. Vomiting and fever may or may not occur, but diarrhea is almost always part of the picture.



Many people feel that any stools "looser" or softer than normal constitute diarrhea. This isn't really the case. Our stools vary in consistency depending on diet: older children and adults may have hard and soft stools in the same day, while infants' stools tend to be looser than older childrens' but still depend on what they are fed. Usually, babies fed breast milk produce looser stools than formula-fed babies, and babies fed soy-based formulas often have firmer stools than those being given milk-based formulas.

We usually define "diarrhea" as stools which are watery or nearly so. "Watery" means that the stool has no "chunks" in it, and, if your child is in diapers, the stool is running out of the diapers. Also, in true diarrhea the child is usually having many (sometimes up to 1-2 per hour) bowel movements. This is a different problem from that of kids who feel like they have to have a bowel movement frequently but don't. The biggest problem with frequent watery stools is the danger of losing so much fluid that you become dehydrated -- in fact we put children with gastroenteritis in the hospital because of severe dehydration, not because of the diarrhea itself.


Strictly speaking, vomiting is a forceful ejection of material from the stomach. It can be caused by stimulation from something (infection or other irritants) in the stomach, on its way to the stomach, or beyond the stomach in the intestines. It can also be caused by many other things, including obstructions in the digestive system (such as pyloric stenosis in very young babies), but here we'll stick to the infections that can cause both vomiting and diarrhea. Many times we will see children who have both vomiting and diarrhea. Besides being really miserable, vomiting makes gastroenteritis harder to treat since a vomiting child cannot keep fluids down and thus becomes dehydrated much faster.


Fever often, but does not always, accompanies gastroenteritis, especially the viral and bacterial types since the body turns up its thermostat to help fight infections. The treatment of a fever in gastroenteritis is often complicated by vomiting, which makes it hard to keep Tylenol or other medicines in the stomach even if you can persuade your child to take them.


You can go without food for quite a while if you have to. Going without water is much more serious.

We normally lose water from our bodies in many ways, including sweating, water contained in the air we exhale (which contains mush more water than the air we inhale, because of evaporation from the lungs and mucous membranes), urine, and water in the stool. To make up for this, we need to take in water constantly to make up for the losses, usually by drinking.

We also produce urine constantly, not only to get rid of excess water but also to flush out various chemicals we don't need any more. (Essentially, the kidneys are chemical filters for your blood.) Since the flushing process requires water, you need to produce at least a little urine all the time. The amount of water in the urine varies depending on whether your body needs to save or get rid of water, but we have to have some water in the urine. Infants produce more urine than older children and adults because their kidneys aren't fully mature and can't save as much water as they can when they're older.

There are several ways to decide whether someone is becoming "dehydrated", or taking in less water than they are putting out. Dry mucous membranes in the mouth, sunken eyes, and (in babies) sunken fontanelles (the "soft spot" on the head), are all signs of dehydration. A more dependable sign, especially since it appears sooner than these symptoms, is a drop in urine output. Normally a child should urinate at least every 6 hours; smaller children probably urinate more often, but 6 hours is the minimum beyond which treatment may be needed. Another sign of dehydration is weight loss over days or hours. Slow weight changes are usually dietary (or due to chronic illness); quick weight loss is usually because of dehydration, and is not good for you even if you're trying to lose weight.

What causes gastroenteritis?

Gastroenteritis in young children is most often due to viral infections. There are many viruses that can produce diarrhea, with or without vomiting: these include the rotaviruses, which we usually see in the wintertime, the enteroviruses, which are more common in summer, and adenoviruses, which can occur year-round but usually cause respiratory problems, although they can cause diarrhea in babies. A now-common cause of gastroenteritis is the Norwalk virus and other noroviruses, first noticed among cruise-ship passengers but now implicated in school or workplace "epidemics".

Generally, once a particular virus infects you, you aren't likely to get it again; but there are many viruses around and it takes a while for a person to have all of them. (Some viruses, including the noroviruses, do not seem to leave the patients they infect immune for life, which is another complication.) Also viruses can mutate (change some of their characteristics) and may be able to infect people who are immune to the "original" form. This kind of change is the reason we need influenza vaccine every year: this year's influenza is almost always a new and improved (from the virus' standpoint) version, and we need new and improved vaccines to help fight them. (And, yes, influenza viruses can cause gastroenteritis, too.)

There are also bacteria that cause gastroenteritis. They aren't as common in the United States and other countries with well-developed plumbing and sanitation systems. However, bacterial gastroenteritis is seen frequently where sanitation isn't as good -- especially anywhere where drinking water may have been tainted by human or animal waste, including rural areas of the US and other developed countries. Bacterial gastroenteritis can also come from contaminated food (for example, Salmonella outbreaks in potato salad or other egg-based dishes, or E. coliO157 in some undercooked meat). Bacterial gastroenteritis is rarer than viral, but sometime won't go away without antibiotics. On the other hand, giving antibiotics to patients with certain kinds of bacterial gastroenteritis may actually make those people into chronic carriers of the bacteria, so we have to be very careful about when and why we give antibiotics even for bacterial gastroenteritis. Often, if we aren't sure that a child has a viral infection, we will try to culture stool samples to see if pathogenic ("bad") bacteria are present. If we find a bacterial cause, the culture results will help us decide whether antibiotics are needed, and which antibiotic is best.

Although we're discussing infectious gastroenteritis on this Web page, I should also mention one "chemical" cause of diarrhea: lactose intolerance. Many people just can't digest lactose (milk sugar) no matter what, unless they take supplementary enzymes to help with digestion or bacteria which are normally harmless but help break the lactose down so the body can finish the process. For a long time we thought that it's very common in viral gastroenteritis to lose your ability to digest lactose for a few days until the infected mucous membrane cells are replaced (you normally grow new mucous membranes in your intestines every 3 days or so). Drinking milk or eating milk-based foods while you can't digest lactose may cause or worsen diarrhea. This doesn't happen in all patients, though, and most doctors now recommend letting your child continue to drink milk and milk-based formulas even with diarrhea -- especially if milk or formula is all your child will drink. Breast milk in particular seems to help children with gastroenteritis, although that may be because of its many other "ingredients" -- including mother's antibodies to many viruses, possibly including the virus that's making the baby sick. Soy formulas do not contain lactose, and some doctors may recommend switching to a soy formula temporarily during a bout of gastroenteritis. (Besides, soy formulas tend to constipate some children, which may also help the diarrhea.)


Although bacterial gastroenteritis is helped by antibiotics, they don't help in cases of the more common viral gastroenteritis -- in fact, antibiotics can cause or worsen diarrhea. Usually we try to make sure a child stays properly hydrated, and wait until the virus has run its course.


Keeping your child well-hydrated is the mainstay of getting him or her over gastroenteritis. We described how to tell if someone is dehydrated above. The important part of treatment is to give fluids that your child will keep down and absorb.

Pedialyte TM and similar "rehydration formulas" consist of water with sugar and certain minerals. The sugar helps provide energy, and the minerals helps the body absorb water better. Unfortunately Pedialyte doesn't taste all that good (I didn't think much of it when I tried it, and most children I know agree.) There are flavoured versions available, but sometimes they aren't all that great-tasting either. Other brands of rehydration fluids (Infalyte, Rehydralyte) may taste better to some people; they certainly taste different. Altough we have occasionally recommended boiling rice in water, pouring off the water, and serving the water (which contains sugars, minerals, and proteins from the rice) to a child with gastroenteritis, we no longer recommend that; there aren't enough minerals or carbohydrates in the rice water for it to be well-absorbed. Giving rice in the cooking water, however, does seem to help.

Many of us have tried to get children to drink Pedialyte by mixing it with other things. The risk here is that changing the sugar/mineral balance will make the fluids harder to absorb. Unsweetened Kool-Aid is fairly safe, since it contains no sugar. Although I've tried it in desperation myself, I do not recommend mixing soda pop into Pedialyte if you can avoid it. The sugar concentration of, for example, PepsiCola will throw the Pedialyte balance way off -- and, in fact, there is so much sugar in most soft drinks that they can act as laxatives and worsen diarrhea. The same holds true for some "sports drinks" (Gatorade is a sports drink, but I'm not sure what its sugar content is). I haven't tried mixing diet soda and Pedialyte; that may be all right but might cause different kinds of problems.

Another fluid you should avoid with severe gastroenteritis is plain water in large amounts. Plain water is not absorbed as well as water with sugar and minerals. More important, since you lose minerals as well as water in diarrhea and plain water doesn't make up for the minerals lost, your mineral balances can be thrown way off -- possibly to the point of having seizures. This is especially likely in small children whose mineral balances can be upset with relatively small (for grown-ups) amounts of water.

If your child is vomiting persistently, it's best not to push fluids very hard -- the results can be frustrating (and a mess) for all concerned. I treat vomiting by waiting about 10-15 minutes after the last feeding attempt, then giving a very small amount of clear liquid (as little as a teaspoon). If this stays down, then give another teaspoon 3-5 minutes later. If that stays down also, then increase the next feeding by 1 teaspoon, and keep increasing the amount until you are giving 2-4 ounces/feeding (depending on your child's size). If your child throws up a feeding, wait about 15 minutes, then resume at one teaspoon per feeding and work up again. Again, watch the urine output -- that's the best indicator of whether you're getting enough fluid in.


As we all know, stool consistency depends largely on what kinds of food we eat even under normal circumstances. Eating the right kinds of foods and avoiding the wrong ones can make a big difference in how fast you get over gastroenteritis.

Usually, clear liquids are the most easily absorbed "food" of all. They also provide extra water (along with minerals) to help prevent dehydration, and they are usually well-tolerated. The best clear liquid is Pedialyte (if your child will actually drink it -- see above). Clear soups (like bouillon) don't work well, because they are often very salty. Tea, even with a little sugar, is actually not very good, since the caffeine in tea is a diuretic (it makes you urinate more -- which you don't want if you're becoming dehydrated). Heavily sugared drinks, like cola, can actually increase diarrhea by drawing water into the stool (that's why we sometimes recommend corn syrup added to formula as a gentle treatment for constipated babies) -- and the caffeine in cola will make you urinate more than usual, just like the caffeine in tea (and coffee, which is usually a very potent diuretic).

Once your child's appetite begins to improve, start giving solid foods again. Traditionally, we have recommended relatively bland foods (bread, rice cereal, apple sauce, and similar foods), but many children can tolerate other foods early in recovery. Sometimes restarting solid foods is a matter of trial and error: if one food makes your child's symptoms worse, try another.


As you may find in other discussions in my Office on the Web, I'm a minimalist when it comes to throwing medicines of any sort at sick children. This is especially true with gastroenteritis. The diarrhea will usually go away in a few days without medicines if you avoid irritating foods. Over-the-counter diarrhea remedies tend to stop the diarrhea without doing anything about the cause. (Remember that we have almost no antibiotics for viruses.) If the problem is a bacterial infection, antibiotics may help, but we have to know what bacteria we're dealing with to pick the right antibiotics. Also remember that antibiotics, by changing the bacterial population in the intestines, can cause diarrhea themselves. And most of the antidiarrhea medicines have side effects -- some of which can be really nasty. In some rare cases antidiarrhea medicines may help, but you should ask your doctor before trying any of them.

When to call for help

Often we can suggest other measures that you can try at home, many of which I've listed above. We may suggest that you take your child to an after-hours clinic or emergency room where a doctor can examine and if needed give fluids IV. (In some bad cases of gastroenteritis the best way to help get a child over the worst part is to give them constant IV fluids until the vomiting and diarrhea go away -- which can sometimes take a couple of days if there's a bad infection involved.)

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PLEASE NOTE: As with all of this Web site, I try to give general answers to common questions my patients and their parents ask me in my (real) office. If you have specific questions about your child you must ask your child's regular doctor. No doctor can give completely accurate advice about a particular child without knowing and examining that child. I will be happy to try and answer general questions about children's health, but unless your child is a regular patient of mine I cannot give you specific advice.

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Copyright © 1996, 1997, 1998, 1999, 2001, 2005, 2007, 2008, 2011, 2013 Vinay N. Reddy, M.D. All rights reserved.
Written 08/20/96; major revision 04/27/05; last revised 09/12/13 counter