Diarrhea (acute gastroenteritis) in children

What is acute gastroenteritis and how common is it?

Gastroenteritis, commonly referred to as “stomach flu,” is essentially diarrhea in a child. The term “acute” means that the illness lasts for up to two weeks. It does not refer to children who have symptoms for three weeks or more, which would be considered chronic diarrhea.
How common is it? Acute gastroenteritis is one of the most frequent illnesses in children. It can occur up to twice a year in infants under the age of 3. It is a common cause of both illness and hospitalization.

What is the definition of diarrhea?

Diarrhea is defined as either a decrease in stool consistency (looser than usual) or an increase in the frequency of bowel movements compared to the child’s normal pattern.
Another widely accepted definition is three or more loose stools per day.

What about other symptoms? Do fever or vomiting have to be present?

Fever may or may not occur—it can be low-grade or high.
Vomiting sometimes appears at the beginning of acute gastroenteritis and may be followed later by diarrhea. However, the presence of vomiting or fever is not required to define the condition as gastroenteritis.

What if the child has only vomiting?

This is important—please take note.
While gastroenteritis may begin with vomiting alone, a child who has only vomiting (with either normal or loose stools), with or without fever, should be evaluated by a pediatrician.
Vomiting can be a symptom of more serious conditions that pediatricians want to rule out, such as a head injury, intestinal obstruction, or severe infection. In fact, pediatricians often feel more comfortable with children who have both vomiting and diarrhea than with those who are only vomiting.

What causes diarrhea (acute gastroenteritis)?

The main causes are viruses, bacteria, and parasites.
Among viruses, Rotavirus used to be the most common cause of diarrhea in young children before the introduction of the vaccine. It typically causes both vomiting and diarrhea and was a major cause of dehydration. Read more about rotavirus and the vaccine here.
In recent years, Norovirus has become a more common cause, though many other viruses can also lead to diarrhea in children.

When it comes to bacteria, the three main pathogens worth mentioning (though not the only ones) are:
1. Campylobacter jejuni – very common
2. Shigella – several strains can cause illness in both children and adults
3. Salmonella – still relatively common, though its prevalence has declined in recent years

Bacterial diarrhea may also be referred to as bacterial colitis or dysentery.
In some parts of the world, parasites are also a frequent cause of acute gastroenteritis in children.

Can you distinguish between the different causes of acute gastroenteritis in children?

Yes and no.
Signs like high fever, blood or mucus in the stool (as opposed to just watery diarrhea), and abdominal pain are more often associated with bacterial pathogens.
Age can also be a clue. A one-year-old child with watery diarrhea is more likely to have a viral infection picked up in daycare than a 15-year-old teenager. Of course, this isn’t always the case, but it’s a helpful indicator.
The most important point to remember is the presence of blood or mucus in the stools. Watery diarrhea often points to a viral cause, while blood or mucus may suggest a bacterial infection. For those with a strong stomach, you’ll find an example image at the end of this post.

How can you prevent gastroenteritis in children?

A few strategies include:
Vaccines – In many countries, the rotavirus vaccine has been part of the routine vaccination schedule for over a decade. It is typically given at 2, 4, and 6 months of age. Rotavirus was the leading cause of diarrhea before the vaccine significantly reduced its prevalence.
Breastfeeding – As a major component of infant nutrition, breastfeeding has been shown to lower the risk of gastroenteritis. Read more about it here.
Daycare attendance – Children in daycare settings are exposed to more infections and therefore have a higher risk of diarrhea.

When should you see a pediatrician?

It’s often hard to provide strict guidelines, so if you’re unsure, always consult a physician. Key scenarios include:
Infants under 2 months with diarrhea must be examined by a physician.
Repeated vomiting – as discussed earlier, this can be a red flag.
Frequent stools – official guidelines mention more than 8 large-volume stools per day. This raises concern for dehydration.
Children with underlying medical conditions – chronic illness increases the risk of dehydration, so prompt medical evaluation is necessary.
Signs of dehydration – see the next section.

What’s important to know about dehydration in children?

It’s a complex topic, but here are some key points:
1– The younger the child, the higher the risk. A 5-month-old with 6 loose stools and vomiting is at greater risk of dehydration than a 5-year-old with the same symptoms.
2– Volume of symptoms matters. While even a few episodes can lead to dehydration, more frequent vomiting and diarrhea generally increase the risk.
3– Vomiting alone vs. diarrhea vs. both – children who vomit can’t retain fluids and become dehydrated faster. Those with only diarrhea may still be able to drink and stay hydrated.
4– Is the child eating or drinking? Pay attention to fluid and food intake. A child who drank soup and ate a small snack is less likely to be dehydrated than one who hasn’t eaten anything.
5– Sugar and salt – dehydrated children often have low blood sugar and electrolyte imbalances. Rehydration treatment should focus on replacing both sugar and salt.

What are the physical signs of dehydration in children?

Here are some of the most important signs:
Weight loss – this is helpful primarily in infants whose recent weight is known or who are weighed regularly at home.
Prolonged capillary refill time – with the child’s hand at heart level, press on a fingertip. If it takes longer than 3 seconds to return to normal color, this may indicate dehydration.
Decreased skin turgor – pinch the skin on the lower abdomen (near the belly button). If it doesn’t return quickly to normal, dehydration may be present (similar to the loss of skin elasticity in the elderly).
Reduced urine output – a child who urinates regularly is less likely to be dehydrated. However, in infants, this may not be reliable, as they can still urinate while dehydrated. It’s also hard to judge in diaper-wearing children since urine and watery stools can look similar.
Other signs include irregular breathing, cold extremities, weak pulse, dry mucous membranes, sunken eyes, no tears when crying, and a generally poor appearance.

Are blood tests necessary for suspected dehydration or gastroenteritis?

A skilled physician’s examination is more important than any lab test.
If a bacterial infection is suspected, the doctor might order a stool culture or stool PCR.
In cases of suspected dehydration, blood tests may be recommended to assess glucose, electrolyte levels, and kidney function.

What is the treatment for children with diarrhea?

There are several steps you can take to reduce your child’s discomfort and lower the risk of hospitalization:
Lower fever – if the child has a high fever, treatment is appropriate. In children with diarrhea who are drinking less, paracetamol (acetaminophen) is preferred over ibuprofen.
Antiemetics (for vomiting) – not commonly used in children but may be considered in certain cases.
Antidiarrheal medications – also rarely used in children.
Probiotics – some bacterial strains have been shown to be helpful, but commercial products vary widely in their bacterial types and concentrations. Routine use is not currently recommended.
Nutrition – in most cases, there’s no need to change formula during the first few days. In children with diarrhea lasting over 5 days or where symptoms have resolved and then returned, temporary lactose avoidance may help. Most formula brands offer lactose-free versions (not necessarily soy-based).
In general, I have not found commercial treatments to be especially helpful. The focus should be on proper fluid and electrolyte replacement, not unnecessary purchases.