Gastroenteritis: Stomach Flu Causes, Symptoms, Diagnosis, Treatment

History

Early observations of gastroenteritis-type diseases date back to the time of Hippocrates (460 – 370 BC). At that time, teething, weaning, and hot temperatures were assumed to contribute to gastroenteritis in infants. But, it was only in 1825 that the term ‘gastroenteritis’ was first used to describe the illness [4].

While gastroenteritis was initially suspected to be a viral infection, it was not confirmed until the late 1960s when an outbreak affected students at an elementary school in Norwalk, Ohio, USA. During this period, the Norovirus (previously called Norwalk virus) was first described. Norovirus is one of the main causative agents of the disease. 50% of the students in Norwalk had the virus in their stool [5]. 

In 1972, the virus was visualized for the first time through immunoelectron microscopy and was found to be small and round in structure [6]. One year later, in 1973, the ‘Rotavirus,’ another source of the stomach flu, was first observed in the small intestines of children with diarrhea through electron microscopy [7]. The virus was named ‘Rotavirus’ because of its wheel-like appearance [1,7]. Within a few years, it was recognized as one of the most common causes of diarrhea in young children worldwide. Nearly one-third of these children had been hospitalized with rotavirus infection [7]. 

Epidemiology

Most viral gastroenteritis cases in the world are caused by norovirus and rotavirus. The rotavirus mainly causes gastroenteritis in children, whereas norovirus can affect people of all ages. Norovirus, in particular, is the cause of some of the notable gastroenteritis outbreaks in the world [3]. 

Young children and the elderly are the ones that are most affected compared to people belonging to other age groups, as they are more vulnerable to dehydration [2]. South Asian countries were found to be largely affected by the disease. The number of gastroenteritis-related deaths in these countries is estimated to be around 7.6 million per year [4]. 

Norovirus-inflicted Gastroenteritis

Norovirus is a single-stranded RNA virus that belongs to the family of calicivirus. Over 90% of gastroenteritis outbreaks worldwide are caused by norovirus. One of the distinguishing characteristics of norovirus is that it can withstand extreme temperatures and is present all throughout the year.

The chances of contracting a norovirus infection are more in closed communities like nursing homes, schools, and military housing quarters. The elderly and people with a weak immune systems may suffer from severe and prolonged illness. In the United States, around 19 to 21 million people get infected by norovirus annually. The US sees around 56,000 to 71,000 hospitalizations and 570 to 800 deaths yearly due to norovirus-related gastroenteritis [1].

Norovirus infections are the leading cause of restaurant outbreaks in the US, responsible for over half of them. The states with the most norovirus outbreaks in the past are Connecticut, Minnesota, New York, Rhode Island, Tennessee, Washington, and Wisconsin [8].

Rotavirus-inflicted Gastroenteritis

Rotavirus is a double-stranded RNA virus. It affects mostly children. Adults who get infected by rotavirus are usually asymptomatic. Rotavirus is responsible for the deaths of over 200,000 children per year worldwide. Nearly 40% of children who were infected were hospitalized [1,3]. In the US, cases peak during the winter, from December to April. However, seasonality has been inconsistent since a vaccine was introduced in 2006. 

The rotavirus vaccine has successfully reduced the number of infections and lowered the severity of the disease. Before the vaccine was introduced, around 3.5 million children were infected every year in the US, and between 55,000 to 70,000 of them were hospitalized.

Since the advent of the vaccine, the US has seen a reduction in the number of cases by 50% to 90% each year, and the number of hospitalizations dropped by 40,000 to 50,000. Although cases have significantly reduced, rotavirus remains one of the leading causes of diarrheal illness in children even today [1].  

How is it Spread?

In general, gastroenteritis is a contagious disease. Norovirus-inflicted gastroenteritis, in particular, is more contagious due to a low infectious dose. This means that only a small amount of the virus is needed to cause an infection. The norovirus can withstand a wide range of temperatures and can be present in the environment for several days. In most cases, the source or origin of the virus is the feces or sometimes the vomit of an infected person. Most of the outbreaks that have occurred in the past were associated with food contaminated with fecal matter [3]. Here are a few ways in which gastroenteritis can spread to people:

Contaminated food

• Gastroenteritis can spread to healthy individuals when they eat food an infected person handles. Particles of feces or vomit on their hands can easily contaminate the food item, causing illness.
• Surfaces with feces or vomit particles on them can also contaminate food when placed on them.
• Meat, vegetables, or fruits washed with contaminated water can also be a source of infection. 

Contaminated water

• Feces of an infected person with a high viral load can enter septic tanks. When people use the water from these tanks or if water leaks out, it can contaminate other freshwater tanks or wells nearby. 
• Water can also get contaminated when people defecate or vomit in it.

Contaminated surfaces

• Surfaces can get contaminated when an infected person touches them with bare hands that have particles of feces or vomit on them.
• While passing stool (especially diarrhea) an infected person can splatter their feces onto the surface of the toilet and pass the infection onto another person. Similarly, vomit can splatter onto the surface of a toilet or wash basin. 
• Surfaces can also be contaminated with food, water, or other objects like kitchen wipes, toilet brushes, etc [9,10].

Biology of the disease

Once the norovirus or rotavirus enters the digestive tract, they affect the enterocytes – absorptive cells that line the inner surface of the small and large intestines. The virus then begins replicating by using resources within the enterocytes. This leads to malabsorption and osmotic diarrhea because the virus interferes with the production of digestive enzymes (brush-border enzymes).

During this process, the virus damages the enterocytes and the intestinal villi, finger-like projections made up of cells that line the small intestine. Without the villi, the intestines do not absorb the right nutrients, no matter how much food is eaten. This condition also results in the loss of intestinal fluids and cell function, and electrolyte abnormalities develop.

Once the virus multiplies and damages the intestines, it is passed through the stool and vomit. The viral load in the stool is usually at its peak one or two days after the onset of the symptoms. In some cases, viral shedding can last for several weeks, even after the symptoms subside [1].

Symptoms

The incubation period of viral gastroenteritis is one to three days. People with a normal immune system recover within two to five days. People with a weak immune systems might take several weeks, months, or even years to recover [3].

Norovirus

In the case of norovirus-inflicted gastroenteritis, disease onset can be abrupt. People usually recover in three days without any lasting issues. The most common symptoms of norovirus-inflicted gastroenteritis are: 

• Abdominal cramps
• Nausea
• Vomiting
• Diarrhea (non-bloody and can occur multiple times per day)

Other symptoms include:

• Muscle pain
• Malaise
• Low-grade fevers

Rotavirus

The symptoms of rotavirus-inflicted gastroenteritis are:

• Severe vomiting
• Diarrhea
• Abdominal pain
• Eating disorder
• Low-grade fevers [1].

Diagnosis

Diagnosing norovirus

• Diagnostic methods to detect the RNA of the virus are used to trace out the norovirus infection. These include end-point RT-PCR and real-time RT-PCR assays.
• Rapid antigen-detection tests and enzyme immunoassays are also widely used to detect the presence of viral antigens. However, the overall sensitivity shown by these methods is quite low [3]. 

Diagnosing rotavirus

• Enzyme immunoassay tests are used to detect the virus in fecal specimens. They show high sensitivity and specificity. They are a commonly used diagnostic method in both clinical and public health laboratories.
• Latex agglutination and lateral flow immunoassays are used to detect antigens. They show high sensitivity when done during the presence of illness.
• Molecular detection methods effectively detect rotavirus with high specificity and sensitivity [3].

Treatment

• Patients with severe illnesses are usually dehydrated. So, medical attention is needed to keep them hydrated [1]. 
• Fluid or rehydration therapy is given to rehydrate patients. For those who are not able to ingest fluids orally, they may be provided intravenously (saline and sodium lactate solutions). In such cases, hospitalization is needed to carefully monitor electrolyte levels [1].
• Probiotics can be given to supplement the fluid therapy. They can be effective in reducing the duration of diarrhea [3].
• Ondansetron or metoclopramide can help patients control vomiting and nausea-related symptoms [1].

Prevention

Currently, the vaccination to help tackle norovirus is in clinical trials [3]. But, the one available for rotavirus is somewhat effective in reducing the severity of the disease in children [11]. The following are a few preventive measures to protect yourselves and your loved ones from viral gastroenteritis:

• Ensure that your child is given the rotavirus vaccine on time – The first dose should be administered before the child is 15 weeks old. The remaining doses should be given before the child is eight months old [10].
• Make it a practice to regularly wash your hands, especially after using the toilet, changing diapers, and before eating, cooking, handling food items, or taking medicines. Also, ensure that your kids do the same.
• Wash vegetables and fruits properly before consuming them. Meat should be properly washed and completely cooked. Since norovirus can survive at extreme temperatures, quick steaming cannot kill the virus.
• An infected person’s best thing is to stop preparing food or providing care for others. Doing this can prevent the infection from being passed on to others.
• Surfaces should be regularly cleaned and disinfected, especially in the kitchen and toilets.
• Clothes should be washed and machine dried at a high temperature [12].