Gastroenteritis, sometimes called stomach flu, is the irritation and inflammation of the lining of the gastrointestinal tract. Acute gastroenteritis is a diarrheal disease with a quick appearance of symptoms. The disease may be mild or severe and may pose a threat to a person’s life. Acute gastroenteritis may be a result of an infection, ingestion of toxins (such as heavy metals or a food allergy), or as a result of certain medications such as cytotoxics (used in cancer therapy).

Infectious acute gastroenteritis may be caused by bacteria, viruses or parasites. Non-infectious acute gastroenteritis may be a result of toxin ingestion or using certain medication. Infectious gastroenteritis is transmitted by different methods including contaminated food or water, the fecal oral route, and through the air. Most commonly, gastroenteritis is caused by viruses such as rotaviruses and bacteria such as Salmonella.

Risk Factors for acquiring acute gastroenteritis include close contact with someone who has gastroenteritis, poor food-handling hygiene, travelling to certain countries and using or drinking contaminated water.

Infectious agents responsible for gastroenteritis cause diarrhea through several mechanisms. These mechanisms result in increased fluid secretion and/or decreased absorption, leading to an increase in the amount of fluid in the intestine. This fluid cannot be sufficiently reabsorbed, so the body excretes it which leads to dehydration and the loss of electrolytes and nutrients.

Signs and symptoms of gastroenteritis cases may differ according to the cause of the disease. Early or prodromal symptoms of viral gastroenteritis include mild fever and vomiting, but the condition quickly advances to include other symptoms such as watery diarrhea and abdominal cramps. Incubation periods vary however symptoms usually begin within 12 to 48 hours and last for 1 to 3 days.

Bacterial cases of gastroenteritis usually present with symptoms of vomiting, diarrhea, and abdominal discomfort. Bloody diarrhea may be present in severe cases.

A swollen abdomen, severe abdominal pain, blood in vomit or stool, vomiting that lasts longer than 48 hours, a fever higher than 40°C and dehydration are all signs and symptoms of severe gastroenteritis.

The first step in diagnosing acute gastroenteritis is collecting patient history, specifically the doctor will ask about when the symptoms first appeared. The severity of the symptoms such as frequency, quantity, and duration of diarrhea and vomiting, in addition to the consistency and color of stools are important information for identifying the cause of gastroenteritis.

A physical examination performed may help the doctor asses the presence and severity of dehydration. Laboratory tests such as a stool sample may be collected when the cause is suspected to be a bacterial or protozoal agent. In cases of severe abdominal pain, imaging tests may be used to rule out other causes of the pain such as appendicitis.

In most cases of gastroenteritis, the disease resolves without medical intervention, which in most cases primarily supportive in nature. Medication may be used to treat the symptoms such as antidiarrheals and medication to prevent vomiting and nausea. In cases with dehydration, oral rehydration therapy is used to return fluid and electrolyte levels to normal.

Most cases of gastroenteritis recover without complications, even without treatment.  However sometimes complications may appear, the most common of which is dehydration.

Gastroenteritis is most commonly spread by the fecal-oral route. Methods to prevent acquiring gastroenteritis include careful hand washing, avoiding use of contaminated water and avoiding consumption of undercooked and raw meats and seafood.

The prognosis for gastroenteritis is generally excellent as most cases recover without the need for medical treatment.

According to a study published in the Journal of Epidemiology, a Japanese publication, viruses were the leading cause of gastroenteritis (41.3%), followed by bacteria (26.8%) and Giardia lamblia (a parasite) (12.4%) 11. In children, viruses account for almost 70% of cases of acute gastroenteritis.

Gastroenteritis, commonly called stomach flu, is the inflammation and irritation of the lining of the gastrointestinal tract. Acute gastroenteritis is a diarrheal disease where the symptoms appear rapidly (sudden onset). Other symptoms accompanying the diarrhea potentially include nausea, vomiting, fever, or abdominal pain. The severity of the disease varies from mild to severe and could potentially be life threatening.

The disease may be infectious, caused by infectious microorganisms such as bacteria, viruses and parasites or may be noninfectious as a result of ingestion of toxins (such as food allergies, heavy-metal poisoning), and drugs such as cytotoxics (used in cancer therapy).

Factors that may cause gastroenteritis include bacteria, viruses, parasites, toxins, and drugs. Infectious gastroenteritis is transmitted via different routes including contaminated food, water borne, the fecal oral route, and in some classes of viruses through the air.

Viruses and bacteria are considered the most common causes for gastroenteritis cases.

The leading causes of bacterial diarrhea worldwide are Salmonella, Shigella, and Campylobacter species, followed by Aeromonas species. Other bacterial species that may cause gastroenteritis include B cereus, C difficile, E. coli (Enterohemorrhagic O157:H7, enterotoxigenic, enteroadherent, enteroinvasive), Clostridium perfringens, Listeria, Plesiomonas species, Providencia, Vibrio cholera, Yersinia enterocolitica, C jejuni, V parahaemolyticus, V vulnificus, and Mavium-intracellulare (MAI) (in immunocompromised patients).

E coli and Clostridium species are normally found in the gastrointestinal tract, however pathogenic strains of these organisms may cause gastroenteritis.

Rotaviruses and noroviruses are the most common viral causes of gastroenteritis. Other viruses that may cause the disease include Caliciviruses, Adenovirus, Parvovirus, Astrovirus, Coronavirus, Pestivirus, Torovirus.Parasitic causes of gastroenteritis include Giardia lamblia, Amebiasis, Cryptosporidium and Cyclospora.

• A weak immune system
• Close contact with someone who has gastroenteritis.
• Poor food-handling hygiene such as not washing hands before preparing or consuming food.
• Poor personal hygiene such as not washing hands properly after using the bathroom.
• Using or drinking contaminated water.
• Age – young children and old people are more susceptible
• Living or being in close contact with a large group of people such as in a dormitory or a school.
• Travel – Travelling to certain countries is associated with the risk of contracting specific species of bacteria that cause gastroenteritis. Enterotoxigenic E coli is the most prevalant cause of traveler's diarrhea. The risk of contracting (catching) diarrhea while traveling is the highest in Africa. South America, South Asia, Spain, Portugal, and Eastern European countries are also associated with a relatively high risk.
• Consuming raw foods, particularly meats and dairy.
• Eating out
• Using public swimming pools
• Exposure to animals (pigs, dogs, cats, turtles)
• Living in a country with a poor sanitation system.

Typically, acute gastroenteritis is caused by infectious agents. These agents cause diarrhea through several mechanisms. These mechanisms result in increased fluid secretion and/or decreased absorption. This causes an increase in the quantity of fluid in the intestine. This fluid cannot be sufficiently reabsorbed, resulting in its excretion from the body, leading to dehydration and the loss of electrolytes and nutrients. Toxins produced by the infectious microorganisms, particularly bacteria cause diarrhea. Some toxins result in watery diarrhea while others cause bloody stools. In most cases the bacteria remain in the gastrointestinal tract however in some cases the bacteria may invade the blood stream causing enteric fevers such as typhoid.

Signs, symptoms and presentation of gastroenteritis cases may differ according to the cause of the disease.

Early or prodromal symptoms of viral gastroenteritis include mild fever and vomiting, but the condition quickly develops to include other symptoms such as watery diarrhea (more than 6 stools in 24 hours) that may last between 1-4 days and abdominal cramps. Incubation periods vary according to the viral microorganism; however symptoms usually begin within 12 to 48 hours and last for 1 to 3 days.

Bacterial gastroenteritis typically appears with symptoms of vomiting, diarrhea, and abdominal discomfort. Severe cases may present with bloody diarrhea.

A swollen abdomen, severe abdominal pain, blood in vomit or stool, vomiting that lasts longer than 48 hours, fever higher than 40°C and dehydration are all signs and symptoms of severe gastroenteritis.

A combination of methods is used to diagnose acute gastroenteritis.

Patient history:

History of presentation or the onset of symptoms is a very important tool for diagnosing gastroenteritis.  

Travel history, exposure to animals and food recall are all important factors in determining the type of microorganism responsible.

In addition, the severity of the symptoms such as the onset (beginning), frequency, quantity, and duration of diarrhea and vomiting, as well as the consistency and color of stools are also important to help determine the cause of gastroenteritis.

Appetite and food consumption during illness, urine output, and weight loss are factors determining dehydration.

Physical examination:

A physical examination may also be performed that may help in determining the cause of gastroenteritis and indicate the presence and degree of dehydration.

Temperature, blood pressure, pulse, and body weight may indicate the severity of the problem. A high fever and/or severe abdominal pain and tenderness usually indicate a bacterial infection. Tachycardia (irregular heartbeat), thready pulse (weak/irregular), and hypotension indicate severe dehydration. Dry mouth, absence of tears, skin tenting (a slow return of the skin to its normal position after being pinched), dry skin, and capillary refill are all signs of dehydration.

Laboratory tests:

If the patient has clear symptoms of viral gastroenteritis, lab tests are not performed.

If a bacterial or protozoal infection is suspected, a stool sample is collected bad tests such as  studies occult blood, microscopy, WBC count, enzyme immunoassay and bacterial culture are performed.

Serum electrolytes, urea, creatinine, amylase, CBC count may be conducted for patients with suspected dehydration.

Other tests:Abdominal imaging studies or a sigmoidoscopy (moving a tube into the rectum to observe the sigmoid colon) may also be performed in cases of severe abdominal pain to rule out other causes of the pain such as appendicitis or inflammatory bowel disease.

Most cases of gastroenteritis are self-limited. Medical care in such cases is mainly supportive in nature. Oral rehydration therapy is used to treat cases of diarrhea if necessary, ensuring proper compensation of lost fluids and electrolytes. If oral rehydration is unsuccessful or if the patient suffers from severe dehydration, intravenous rehydration is used.

Antiemetics (drugs to prevent vomiting and nausea) may be used to treat adults. They are usually not recommended in children.

Antidiarrheals (antimotility agents) these medications are usually not recommended; however, they may be used in the treatment of mild-to-moderate diarrhea, particularly with nonbloody and traveler's diarrhea.

Antibiotics may be prescribed for cases of bacterial gastroenteritis.

Antiprotozoal medication may be prescribed for cases of protozoal infections.

Dietary adjustments include increasing the consumption of clear fluids in small doses at a time. Flat colas or ginger ale (with no fizz) are good sources. Jell-O and popsicles are also good alternative sources of fluids, particularly in children.

Following the BRAT diet (ie, bananas, rice, applesauce, and toast) may help.

Foods rich in electrolytes and complex carbohydrates, such as potatoes and lean meats (chicken, fish) help replenish nutrients lost by diarrhea and vomiting. Electrolyte and fluid replacement solutions may also be purchased at grocery stores and pharmacies.

Most cases of gastroenteritis recover without complications, even without treatment.

Dehydration is the most common complication of viral gastroenteritis and other diarrheal diseases. Metabolic acidosis, electrolyte disturbance (hypernatraemia, hyponatraemia, hypokalaemia), carbohydrate intolerance (lactose, glucose), susceptibility to reinfection, development of food intolerance (cow's milk, soy protein), haemolytic uraemic syndrome, iatrogenic complications (complications caused by a healthcare provider) due to inappropriate composition or amount of intravenous fluids, and in severe cases, death, are other possible complications.

Gastroenteritis is usually spread by the fecal-oral route. Prevention entails careful hand washing, proper disposal of diapers, careful preparation and proper storage of food and beverages, Avoiding undercooked meats and seafood, contaminated water. Other prevention methods include avoiding contact with infected people, close contact with animals, and use of public swimming pools.

Rotavirus oral vaccine is recommended by the WHO and American Academy of Pediatrics for all children globally.

Salmonella typhi vaccine is recommended for travelers to countries with a high incidence of typhoid fever.

In countries that suffer from a high prevalence of cholera, children take the oral cholera vaccine.

Most cases of gastroenteritis recover without treatment if the with proper disease management, as such the prognosis for gastroenteritis is generally excellent.

Patients who develop severe dehydration and secondary malnutrition from an extended period of disease are at high mortality risk. Neonates and young infants have the highest risk for dehydration, malnutrition, and malabsorption syndromes.

The prognosis for patients with severe underlying medical conditions and those living in countries where medical care is inadequate is less optimistic.

Acute gastroenteritis is a very common disease. It results in significant mortality and morbidity worldwide.

According to a study published in the Journal of Epidemiology, a Japanese publication, viruses were the leading cause of gastroenteritis (41.3%), followed by bacteria (26.8%) and Giardia lamblia (a parasite) (12.4%). In children, viruses account for almost 70% of cases of acute gastroenteritis.