What is viral gastroenteritis?
Viral gastroenteritis is an infection of stomach and intestinal lining caused by a virus leading to watery diarrhea and vomiting. It is commonly referred to as the stomach flu or gastric flu. Viral gastroenteritis is a very common and highly contagious infection which tends to cause small outbreaks in day care centers, schools, workplaces and communities. It may range from mild to severe depending upon the type and duration of the infection. Viral gastroenteritis is largely a self limiting infection that tends to resolve on its own. However, in severe cases associated with excessive loss of fluid and electrolytes in the vomitus and stool, dehydration can be a major complication that may require hospitalization.
There are several different types of viruses that can cause gastroenteritis. By attaching to and entering the cells lining the villi of the small intestine (enterocytes), the viruses can causes fluids and salts to pass out into the intestinal (lumen). There is evidence to suggest that some viruses contain non-structural proteins which cause this transudation thereby acting as an enterotoxin. The viruses replicate within the intestinal cells eventually exiting where it may or may not cause the destruction of the intestinal cells. Inflammation may also upset digestion and subsequent absorption of nutrients like carbohydrates which then act as solutes and draws water into the intestinal lumen. Irritation of the epithelial lining with water and electrolyte transudation into the lumen manifests as vomiting and watery diarrhea. Blood and mucus in the stools are not common with viral gastroenteritis although it may be seen with certain severe types of bacterial gastroenteritis.
Types of Stomach Flu Viruses
While there are a number of different viruses that can cause viral gastroenteritis, the majority of cases are due to four types of viruses. All of these viruses are transmitted by feco-oral route.
- Rotavirus is the most common virus causing gastroenteritis, especially in infants under 18 months of age. The infection is usually milder in adults. The clinical symptoms appear after 1 to 3 days after exposure and typically causes vomiting and watery diarrhea lasting for 3 to 8 days associated with fever and abdominal pain.
- Adenovirus commonly causes gastroenteritis in children less than 4 years of age. The incubation period is about 3 to 10 days and diarrhea lasts for 10 to 14 days.
- Calicivirus causes gastroenteritis in all age groups and is the most common gastroeneteritis virus in adults. The incubation period lasts about 24 hours and the symptoms like vomiting and diarrhea lasts less than 3 days. Immunocompromised individuals are at a greater risk.
- Astrovirus infects infants and young children primarily but adults can also be infected. The clinical symptoms appear after 3 to 5 days of exposure and lasts for about 3 to 7 days. The infection can occur at any time during the year but it is more active during the winter months.
Causes and Risks
Viral gastroenteritis is caused by an infection with certain viruses that have an affinity for the tissue lining the gastrointestinal tract. The major risk for viral gastroenteritis is the consumption of contaminated water and food which is spread via the feco-oral route.
Food is usually contaminated when an infected person makes contact with food and water and contaminating it. This risk is drastically minimized with proper hygiene practices like washing the hands regularly and thoroughly particularly after using the toilet. A person who prepares or handles food is more likely to contaminate food. The risk is also greater with the consumption of raw or undercooked shellfish which are harvested from contaminated water source. Partially cooked meat and raw fruits or vegetables that come in contact with contaminated water or other foods are also a risk. Consumption of water contaminated by sewage can be a source of infection.
In viral gastroenteritis, the risk of infection is increased if a person comes in contact with body wastes of an infected person like the vomitus and stool. Caregivers and health workers have to therefore be extra cautious. The young, elderly and people with suppressed immune system have the highest risk of contracting the infection and suffering with complications.
Signs and Symptoms
The common symptoms of viral gastroenteritis include watery diarrhea, nausea and vomiting, abdominal cramps and pain. In some cases it may be associated with fever, headache, myalgia ( muscle pain) and blood and mucus with stools. On average the symptoms start about 12 to 48 hours after contracting the infection and symptoms can vary between 1 to 7 days depending on the type of virus that causes the infection.
In severe cases the patient may develop dehydration which may be clinically evident by the following signs and symptoms :
- Dry tongue / mouth.
- Decreased consciousness.
- Low blood pressure with episodes of fainting (syncope).
- Low / absent urine output.
- Soft skull (sunken fontanelles) in infants.
- Sunken eye.
- Decreased skin turgor.
- Skin rashes may also develop as a complication of dehydration.
Clinical evaluation is usually sufficient to make the diagnosis in majority of the cases. If the symptoms worsen or the patient does not respond to conservative treatment of fluids and symptomatic care, then further investigations should be carried out. Testing stool samples may help to rule out any bacterial infection. In cases of severe dehydration the urea, electrolyte and creatinine levels should also be monitored to avoid renal failure.
Viral gastroenteritis will resolve on its own. The goal of the treatment is to prevent and treat dehydration. Fluids and electrolytes that are lost during vomiting and diarrhea should be replenished by oral rehydration therapy. If the patient is not able to tolerate the fluid orally or if comatose then intravenous administration of fluids may be necessary. Anti diarrheal medication like loperamide are not indicated in children but adults may use it after consulting with a doctor. Antibiotics are not indicated in viral gastroenteritis.
Some beverages to be avoided are fruit juices, plain glucose solution, sodas and cola drinks. These drinks contain sugar in large quantities which may cause osmotic diarrhea. Once vomiting stops, a BRAT diet should be commenced and balanced bland meals should be followed soon thereafter even if diarrhea is present. Breast feeding should be continued in children.
It is important to be extra cautious at times of outbreaks or when coming in contact with an infected person. Thoroughly washing the hands, avoiding touching the mouth unnecessarily and eating only in reputable food establishments are important measures to avoid viral gastroenteritis. Water should only be consumed if it is acquired from safe sources. Parents and caregivers of infants with viral gastroenteritis need to wash their hands thoroughly after changing diapers. A rotavirus vaccine may be helpful for infants.