Acute diarrhea in children in Europe is mostly viral, and most cases need no microbiological diagnosis. The bacterial minority matters out of proportion to its frequency, because those are the children who become septic, the children in whom an antibiotic either helps or harms, and the children whose stools need to be cultured.
Who causes what
A pathogenic enteric organism can be isolated from the stool of roughly 45–75% of children with acute gastroenteritis, depending on how intensively the search is made. Rotavirus is the most frequent single agent across Europe. Norovirus, long in second place, is becoming the leading cause of medically attended gastroenteritis in countries with high rotavirus vaccine coverage and accounts for around 10–15% of hospital admissions for acute gastroenteritis in European children. Bacterial causes are less common overall, led by Campylobacter or Salmonella depending on the country. Protozoa are uncommon: carriage of Giardia or Cryptosporidium in European day-care settings is around 1–3% and is frequently asymptomatic.
Precise percentages for how often each cause accounts for community cases vary with country, age, season and vaccine coverage, so the more useful structure is the pattern each class produces.
The pattern each class produces
The patterns follow the part of the bowel an organism affects. Organisms that act on the small bowel — viruses that damage its lining, or enterotoxigenic E. coli, which releases an enterotoxin that makes the intestine secrete fluid — produce watery diarrhea. Organisms that injure the colon produce a colitic pattern, from colitis, meaning inflammation of the colon. A third group tends to cause a protracted illness rather than an acute one.
| Pattern | Typical organisms | Clinical picture |
|---|---|---|
| Watery, small-bowel | Rotavirus, norovirus, adenovirus, enterotoxigenic E. coli | Watery diarrhea, vomiting, no blood |
| Colitic | Shigella, Campylobacter, Salmonella, Shiga toxin-producing E. coli | Frequent small-volume stools, blood or mucus, fever, abdominal pain |
| Protracted | Giardia, Cryptosporidium, enteroaggregative E. coli | Persistent rather than acute; belongs to a different workup |
Within the watery group the viruses are not interchangeable. Rotavirus sits at the severe end: compared with other viral infections it produces higher fever, more diarrheal episodes and longer-lasting diarrhea. Norovirus behaves differently again — vomiting predominates, and may be frequent and severe.
Blood in the stool shifts the differential towards an invasive bacterial cause, but the colitic pattern is not a diagnosis. Shiga toxin-producing E. coli (STEC), named for the Shiga toxin it produces, is the standard counterexample: bloody diarrhea with low or no fever is typical of it, and antibiotics are not recommended unless the epidemiology suggests shigellosis. The reasoning behind that exception is covered in Refeeding and Drug Therapy in Acute Diarrhea.
Separating bacterial from viral at the bedside
High-grade fever with numerous small-volume bloody stools, abdominal pain and systemic upset favour a bacterial colitis. Vomiting and respiratory symptoms favour a viral illness. These are tendencies, not diagnostics: which tests are worth ordering, and when microbiological investigation is worth considering, are covered in Investigations in Acute Diarrhea and Dehydration.
Risk factors for severe dehydration
Whatever the organism, the danger to the child is the fluid loss, and host factors predict deterioration better than the identity of the organism. Younger age, inadequate intake during the illness, and an underlying chronic disease or immune deficiency all raise the risk.
The younger infant is at higher risk mainly because of immune immaturity and feeding mode rather than because the gut mucosa is immature — the intestinal mucosa is functional early in life. Breast milk supplies secretory IgA (the antibody class secreted onto mucosal surfaces), lactoferrin, oligosaccharides and a microbiota that protect against enteric infection, which is why predominantly breast-fed infants have a lower risk of severe or prolonged diarrhea. Children with immunodeficiency, inflammatory bowel disease, renal disease or other chronic conditions start from a higher baseline, and day-care attendance increases exposure.
The effect of feeding practice is large enough to appear directly in odds-ratio data. The figures below come from a case-control study, which compares children who developed the outcome — here, dehydration — with children who did not; an odds ratio above 1 means the factor was more common among the children who became dehydrated.
| Risk factor | Odds ratio | Source |
|---|---|---|
| Withdrawal of breastfeeding during the diarrheal illness | 6.8 | Bhattacharya 1995 |
| More than 8 stools per day | 4.1 | Bhattacharya 1995 |
| Severe undernutrition | 3.1 | Bhattacharya 1995 |
| Age 12 months or under | 2.7 | Bhattacharya 1995 |
| More than 2 vomiting episodes per day | 2.4 | Bhattacharya 1995 |
| No oral rehydration solution given during the illness | 2.1 | Bhattacharya 1995 |
All six come from a single case-control study of 379 children under 2 years with acute watery diarrhea, and they describe associations in that population rather than universal multipliers.
The two most modifiable entries are the last and the first. Oral rehydration solution given early reduces the risk of reaching hospital with a serious deficit, and stopping breastfeeding during the illness does the opposite — breastfeeding continues throughout rehydration and throughout any dietary modification, for reasons set out in Refeeding and Drug Therapy in Acute Diarrhea.
Risk factors say which children are more likely to become severely dehydrated. Whether a particular child already is, and how badly, is judged at the bedside, as described in Clinical Assessment of Acute Diarrhea and Dehydration.