Gastroenteritis

Gastroenteritis is an inflammation of the stomach and intestines, often called infectious diarrhea. It typically causes diarrhea, vomiting, and abdominal pain, sometimes with fever, fatigue, and dehydration. Symptoms usually last less than two weeks. Despite being unrelated to influenza, it is commonly called "stomach flu" in Canada and the United States.

Viruses are the most frequent cause, but bacteria, parasites, and fungi can also trigger it. In children, rotavirus is the main cause of severe illness; in adults, norovirus and Campylobacter are common. The infection spreads through contaminated food or water, or close contact with an infected person. Diagnosis is often unnecessary because treatment is the same regardless of the specific cause.

Prevention in impoverished areas includes hand washing with soap, drinking clean water, breastfeeding instead of using formula, and proper waste disposal. The rotavirus vaccine is recommended for children. Treatment focuses on fluid replacement. Mild to moderate cases can be managed with oral rehydration solution—water mixed with salts and sugar. Breastfeeding should continue during illness. Severe cases may require intravenous fluids or fluids via a nasogastric tube. Zinc supplements are advised for children. Antibiotics are generally not needed, except for young children with fever and bloody diarrhea.

In 2021, there were 4.67 billion cases globally, leading to 1.17 million deaths. Children and people in developing countries are most affected. In 2011, about 1.7 billion cases occurred, resulting in roughly 700,000 deaths in children under five. In the developing world, children under two often experience six or more infections per year. Adults are less affected, partly due to acquired immunity.

**Signs and symptoms**

Gastroenteritis usually includes both diarrhea and vomiting, though sometimes only one appears, often with abdominal cramps. Symptoms start 12 to 72 hours after exposure. Viral cases typically resolve within a week and may involve fever, fatigue, headache, and muscle pain. Bloody stool suggests a bacterial rather than viral cause. Some bacterial infections cause severe abdominal pain and can last several weeks.

Children with rotavirus usually recover fully in three to eight days. Dehydration is a common complication. In severe dehydration, skin pressed slowly returns to its original color and position (prolonged capillary refill and poor skin turgor), and breathing may become abnormal. Repeated infections are common in areas with poor sanitation and malnutrition, potentially leading to stunted growth and long-term cognitive delays.

Reactive arthritis occurs in about 1% of people after Campylobacter infection, and Guillain–Barré syndrome in 0.1%. Hemolytic uremic syndrome (HUS) can follow infection with Shiga toxin-producing E. coli or Shigella, causing low platelets, poor kidney function, and low red blood cell count from breakdown. Children are more prone to HUS than adults. Some viral infections can trigger benign infantile seizures.

**Cause**

Viruses—especially rotavirus in children and norovirus in adults—along with E. coli and Campylobacter, are the main causes. Many other infectious agents, including parasites and fungi, can also cause it. Non-infectious causes are less common. Children face higher risk due to lack of immunity and poorer hygiene habits, particularly in areas without easy access to water and soap.

**Viral**

Rotavirus, norovirus, adenovirus, and astrovirus cause viral gastroenteritis. Rotavirus is the most common cause in children, with similar rates in developed and developing countries. Viruses cause about 70% of infectious diarrhea in children. Rotavirus is less common in adults due to immunity. Norovirus accounts for about 18% of all cases overall. In developed countries, viral gastroenteritis makes up 21–40% of infectious diarrhea cases.

Norovirus is the leading cause of gastroenteritis among American adults, responsible for about 90% of viral outbreaks. These outbreaks often occur in close-contact settings like cruise ships, hospitals, and restaurants. People can remain infectious even after diarrhea stops. Norovirus causes about 10% of cases in children.

**Bacterial**

In some countries, Campylobacter jejuni is the primary bacterial cause, with half of cases linked to poultry exposure. Bacteria cause about 15% of childhood cases, most commonly E. coli, Salmonella, Shigella, and Campylobacter. Food left at room temperature for hours allows bacteria to multiply, raising infection risk. Common sources include raw or undercooked meat, poultry, seafood, and eggs.