Stomach Flu – Causes, Symptoms, Diagnosis, Treatment

Stomach Flu/The word “gastroenteritis” originates from the Greek word gaston, meaning “stomach,” and enteron, meaning “small intestine.” So the word “gastroenteritis” means “inflammation of the stomach and small intestine.” Medically, gastroenteritis is defined as diarrheal disease, in other words, an increase in bowel movement frequency with or without vomiting, fever, and abdominal pain. An increase in bowel movement frequency is defined by three or more watery or loose bowel movements in 24 hours or at least 200 grams of stool per day.

Gastroenteritis, also known as infectious diarrhea and gastro, is inflammation of the gastrointestinal tract—the stomach and small intestine. Symptoms may include diarrhea, vomiting, and abdominal pain.^[rx] Fever, lack of energy and dehydration may also occur. This typically lasts less than two weeks.^[rx] It is not related to influenza, though it has erroneously been called the “stomach flu“.^[rx]

Types of Stomach Flu

It is classified in many ways, but according to the duration of symptoms, it is described as acute, persistent, chronic, or recurrent.

• Acute: 14 days or fewer than 14 days in duration.
• Persistent: More than 14 but fewer than 30 days in duration.
• Chronic: More than 30 days in duration.
• Recurrent: Diarrhea that recurs after 7 days without diarrhea.[rx]

Pathophysiology

The gut bacteria cause diarrhea by different mechanisms including adherence, mucosal invasion, and toxin production. Knowledge of pathophysiology and the mechanism of these pathogenic strategies also help in the evaluation and management of the disease. One of the main functions of the small intestine is to absorb fluids. With the disorder of the small intestine, the fluid does not get absorbed properly, and the action of different toxins causes the intestinal lining to start excreting fluid which results in relatively loose or watery stools.

Inoculum size is one of the important virulence factors that cause pathology. For Shigella and enterohemorrhagic Escherichia coli (EHEC), at a minimum of 10–100 bacteria can cause infection, while one hundred thousand or one million of Vibrio cholerae bacteria are required to cause infection. For this reason, infective doses of different pathogens differ in a great range and depend on the host as well as bacteria.

Adherence is another virulence factor for enteric pathogens. Some bacteria need to adhere themselves to the mucosal lining of the gastrointestinal tract initially. They produce various adhesins and other cell-surface proteins which help them to attach to intestinal cells. V. cholerae, for example, adheres to the brush border of small-intestinal enterocytes via specific surface adhesins, including the toxin-coregulated pilus and other accessory colonization factors. Enterotoxigenic E. coli, which causes watery diarrhea, produces an adherence protein called colonization factor antigen. This is necessary for colonization of the upper small intestine by the organism before the production of enterotoxin, causing disease.

Both cytotoxin production and bacterial invasion and destruction of intestinal mucosal cells can cause dysentery. Shigella and enteroinvasive E. coli infections are characterized by the organisms’ invasion of mucosal epithelial cells, intraepithelial multiplication, and subsequent spread to adjacent cells.

Toxin production is another important virulence factor. These toxins include enterotoxins, which cause watery diarrhea by acting directly on secretory mechanisms in the intestinal mucosa, and cytotoxins, which destroy mucosal cells and associated inflammatory diarrhea.[rx]

Causes of Stomach Flu

Causes of gastroenteritis include bacterial, viral, fungal, and parasitic, but this article will focus on bacterial causes. Causes of infectious diarrhea vary among different geographical regions, urban to rural areas, and depend on co-morbidities and host immune status. However, the most common cause of acute infectious diarrhea are viruses (norovirus, rotavirus, adenovirus, and others). This is indicated by the observation that stool cultures are positive in less than 5% of cases in most studies. Other than norovirus, important causes of watery diarrhea include Clostridium perfringens, and enterotoxigenic Escherichia coli (ETEC). Bacterial causes are more responsible for severe cases of infectious diarrhea than other infectious etiologies. For example, a single study found that in otherwise healthy adults with diagnosed severe diarrheal illness, defined as greater than or equal to four watery/loose stools per day for 3 or more days, a bacterial pathogen was identified in 87% of cases. Among these severe bacterial causes, nontyphoidal Salmonella and Campylobacter spp are the most common causes in the United States. The incidence rate per 100,000 persons in 2016 was estimated by the Centers for Disease Control and Prevention controlled active surveillance program, FoodNet, survey with results as follows:

• Salmonella – 15.4
• Campylobacter – 11.8
• Shigella – 4.6
• Shiga toxin-producing E. coli – 2.8
• Vibrio – 0.45
• Yersinia – 0.42
• Listeria – 0.26[rx]

Some of the common types of infectious gastroenteritis include:

• Escherichia coli infection – this is a common problem for travellers to countries with poor sanitation. Infection is caused by drinking contaminated water or eating contaminated raw fruits and vegetables
• Campylobacter infection – the bacteria are found in animal faeces (poo) and uncooked meat, particularly poultry. Infection is caused by, for example, consuming contaminated food or water, eating undercooked meat (especially chicken), and not washing your hands after handling infected animals
• Cryptosporidium infection – parasites are found in the bowels of humans and animals. Infection is caused by, for example, swimming in a contaminated pool and accidentally swallowing water, or through contact with infected animals. An infected person may spread the parasites to food or surfaces if they don’t wash their hands after going to the toilet
• giardiasis – parasite infection of the bowel. Infection is caused by, for example, drinking contaminated water, handling infected animals or changing the nappy of an infected baby and not washing your hands afterwards.
• salmonellosis – bacteria are found in animal faeces. Infection is caused by eating contaminated food or handling infected animals. An infected person may also spread the bacteria to other people or surfaces by not washing their hands properly
• shigellosis – bacteria are found in human faeces. An infected person may spread the bacteria to food or surfaces if they don’t wash their hands after going to the toilet
• viral gastroenteritis – infection is caused by person-to-person contact such as touching contaminated hands, feces or vomit, or by drinking contaminated water or food.

Symptoms of Stomach Flu

Although it’s commonly called stomach flu, gastroenteritis isn’t the same as influenza. Real flu (influenza) affects only your respiratory system — your nose, throat, and lungs. Gastroenteritis, on the other hand, attacks your intestines, causing signs and symptoms, such as:

• Watery, usually nonbloody diarrhea — bloody diarrhea usually means you have a different, more severe infection
• Symptoms of gastroenteritis include diarrhea, abdominal pain, vomiting, headache, fever, and chills. Most people recover with no treatment.
• Abdominal cramps and pain
• Nausea, vomiting or both
• Occasional muscle aches or headache
• Low-grade fever
• loss of appetite
• bloating
• nausea
• vomiting
• abdominal cramps
• abdominal pain
• diarrhoea
• bloody stools (poo) – in some cases
• pus in the stools – in some cases
• generally feeling unwell, including lethargy and body aches.

Depending on the cause, viral gastroenteritis symptoms may appear within one to three days after you’re infected and can range from mild to severe. Symptoms usually last just a day or two, but occasionally they may persist as long as 10 days.

Because the symptoms are similar, it’s easy to confuse viral diarrhea with diarrhea caused by bacteria, such as Clostridium difficile, salmonella and E. coli, or parasites, such as giardia.

For infants and children

See your doctor right away if your child:

• Has a fever of 102 F (38.9 C) or higher
• Seems lethargic or very irritable
• Is in a lot of discomfort or pain
• Has bloody diarrhea
• Seems dehydrated — watch for signs of dehydration in sick infants and children by comparing how much they drink and urinate with how much is normal for them

If you have an infant, remember that while spitting up may be an everyday occurrence for your baby, vomiting is not. Babies vomit for a variety of reasons, many of which may require medical attention.

Diagnosis of Stomach Flu

GI infectious diseases can cause mucosal inflammation which represents various patterns of tissue response. Histologic patterns of GI infections can be classified as follows:

• Infections producing minimal or no histologic changes (e.g., Vibrio species)
• Infections producing nonspecific inflammation (e.g., Campylobacter jejuni)
• Infections with suggestive/diagnostic features (e.g., pseudomembranes, etc.)

Campylobacter jejuni, Shigella spp, Salmonella spp, Yersinia and E. coli and few other pathogens all have resembling histopathology. The histopathological picture shows a thick layer of mucosa and cluster of bacteria plus neutrophils in the intraepithelial surface; neutrophils accumulate in the lumen and the basal part of the intestinal crypts as well.[5]

History and Physical

The most common history findings for a patient with gastroenteritis are as follows:

• Nausea
• Diarrhea (watery or bloody in dysentery)
• Vomiting
• Abdominal pain
• Fever (suggests an invasive organism as the cause)

On physical examination, the abdomen would be soft, but there may be voluntary guarding. Palpation may elicit mild to moderate tenderness. Fever suggests the cause is invasive pathogens. Signs of dehydration are the most important thing to look for while performing the physical examination; some cases may be alarming and help to identify that which patient needs hospitalization. The following are red flags:

• Dry mucous membranes (dry mouth)
• Decreased skin turgor
• Altered mental status
• Tachycardia
• Hypotension, orthostasis
• Bloody stools
• Recent hospitalization or antibiotics
• Age greater than 65 years
• Comorbidities such as HIV and diabetes[rx]

Evaluation

• Initial evaluation requires good history taking and physical exam – particularly food and medical history, an assessment of duration, frequency, current volume status, and any other alarming signs and symptoms of the patient. Many cases of acute bacterial gastroenteritis may not require any testing to determine a specific etiology, but in a case of severe volume depletion, a serum electrolyte panel should be indicated to check for any electrolyte derangements. A complete blood count cannot distinguish between bacterial etiologies but helps in suggesting severe disease or potential complications, for example, a high white blood count indicates invasive bacteria or pseudomembranous colitis and low platelets counts indicate the development of the hemolytic-uremic syndrome. Blood culture should be obtained in a patient with high fever or other severe constitutional symptoms.
• Stool testing – for bacterial pathogens is indicated in the presence of severe illness (e.g., signs of dehydration/hypovolemia, severe abdominal pain, or need for hospitalization) high-risk host features (e.g., pregnant women, age greater than 70 years, immunocompromised state, or other co-morbidities), and other signs and symptoms of inflammatory diarrhea (e.g., mucus or blood in diarrhea, high-grade fever). A routine stool culture can identify three common bacteria: Salmonella, Campylobacter, and Shigella. Suspicion of other bacterial pathogens (e.g., Vibrio, Yersinia, Aeromonas, and Listeria) should warrant specific microbiology and culture analysis. In case of bloody diarrhea, additional testing for Shiga toxin and leukocytes in stool for EHEC should be ordered in addition to stool culture. In case of persistent diarrhea, the practitioner should send stool samples for ova and parasite testing.[rx]
• Sigmoidoscopy – A doctor inserts a thin, flexible tube with a tiny camera from the anus into the lower large intestine to look for signs of inflammatory bowel disease. The sigmoidoscopy is a 15-minute procedure that doesn’t usually require sedation.

Treatment of Stomach Flu

The majority of cases of noninflammatory diarrhea are self-limited.

Gastroenteritis is usually an acute and self-limiting disease that does not require medication.^[rx] The preferred treatment in those with mild to moderate dehydration is oral rehydration therapy (ORT).^[rx] For children at risk of dehydration from vomiting, taking a single dose of the anti vomiting medication metoclopramide or ondansetron may be helpful,^[rx] and butylscopolamine is useful in treating abdominal pain.^[rx]

Rehydration

The primary treatment of gastroenteritis in both children and adults is rehydration. This is preferably achieved by drinking rehydration solution, although intravenous delivery may be required if there is a decreased level of consciousness or if dehydration is severe. Drinking replacement therapy products made with complex carbohydrates (i.e. those made from wheat or rice) may be superior to those based on simple sugars.^[rx] Drinks especially high in simple sugars, such as soft drinks and fruit juices, are not recommended in children under 5 years of age as they may increase diarrhea.^[rx] Plain water may be used if more specific ORT preparations are unavailable or the person is not willing to drink them.^[rx] A nasogastric tube can be used in young children to administer fluids if warranted.^[rx] In those who require intravenous fluids, one to four hours’ worth is often sufficient.^[rx]

Dietary

It is recommended that breast-fed infants continue to be nursed in the usual fashion and that formula-fed infants continue their formula immediately after rehydration with ORT.^[rx] Lactose-free or lactose-reduced formulas usually are not necessary.^[rx] Children should continue their usual diet during episodes of diarrhea with the exception that foods high in simple sugars should be avoided.^[rx] The BRAT diet (bananas, rice, applesauce, toast and tea) is no longer recommended, as it contains insufficient nutrients and has no benefit over normal feeding.^[rx]

Some probiotics have been shown to be beneficial in reducing both the duration of illness and the frequency of stools.^[rx][rx] They may also be useful in preventing and treating antibiotic-associated diarrhea.^[rx] Fermented milk products (such as yogurt) are similarly beneficial.^[rx] Zinc supplementation appears to be effective in both treating and preventing diarrhea among children in the developing world.^[rx]

Antiemetics

Antiemetic medications may be helpful for treating vomiting in children. Ondansetron has some utility, with a single dose being associated with less need for intravenous fluids, fewer hospitalizations, and decreased vomiting.^[rx][rx] Metoclopramide might also be helpful.^[rx] However, the use of ondansetron might possibly be linked to an increased rate of return to hospital in children.^[rx] The intravenous preparation of ondansetron may be given orally if clinical judgment warrants.^[rx] Dimenhydrinate, while reducing vomiting, does not appear to have a significant clinical benefit.^[rx]

Antibiotics

Antibiotics are not usually used for gastroenteritis, although they are sometimes recommended if symptoms are particularly severe^[rx] or if a susceptible bacterial cause is isolated or suspected.^[rx] If antibiotics are to be employed, a macrolide (such as azithromycin) is preferred over a fluoroquinolone due to higher rates of resistance to the latter.^[rx] Pseudomembranous colitis, usually caused by antibiotic use, is managed by discontinuing the causative agent and treating it with either metronidazole or vancomycin.^[rx]

Antibiotic therapy – Not every patient, even with a known bacterial etiology, should be given antibiotic therapy, especially with Shiga toxin-producing E. coli. Empiric antibiotic therapy with azithromycin or fluoroquinolones can be indicated in severe illness (e.g., greater than 6 stools in a day, fever, need for hospitalization), specific host factors (e.g., age greater than 70 years, immunocompromised host, having co-morbidities), and features suggesting of the invasive organisms (e.g., blood or mucus in stool) but should be discontinued if EHEC is isolated. Tetracyclines have the greatest efficacy for Vibrio. For pregnant patients with the suspicion of Listeria, ampicillin is the drug of choice. For C. difficile infection (CDI), discontinuation of the causative antibiotic and antibiotic therapy should be initiated. It should be noted that the recent Centers for Disease Control and Prevention guidelines changed in March 2018 and now recommend either oral vancomycin or fidaxomicin for nonsevere over oral metronidazole for severe CDI. Combination therapy of oral vancomycin with IV metronidazole should be used for fulminant CDI.

Antimotility agents

Antimotility medication has a theoretical risk of causing complications, and although clinical experience has shown this to be unlikely,^[rx] these drugs are discouraged in people with bloody diarrhea or diarrhea that is complicated by fever.^[rx] Loperamide, an opioid analog, is commonly used for the symptomatic treatment of diarrhea.^[rx] Loperamide is not recommended in children, however, as it may cross the immature blood-brain barrier and cause toxicity. Bismuth subsalicylate, an insoluble complex of trivalent bismuth and salicylate, can be used in mild to moderate cases,^[rx] but salicylate toxicity is theoretically possible.^[rx]

Supportive management

Symptomatic therapy

Complications

Dehydration and depletion of electrolytes are the most common complications above all. Other complications that are common after acute gastroenteritis are the transformation of acute into chronic diarrhea which can lead to lactose intolerance or small-bowel bacterial overgrowth. Some other post-diarrhea complications include exacerbation of inflammatory bowel disease, septicemia, enteric fever, and Guillain-Barre syndrome, a complication likely after Campylobacter infection. Reactive arthritis may occur, particularly after Shigella, Salmonella, Campylobacter, or Yersinia.[rx]

Prevention

The best way to prevent the spread of intestinal infections is to follow these precautions:

• Get your child vaccinated. A vaccine against gastroenteritis caused by the rotavirus is available in some countries, including the United States. Given to children in the first year of life, the vaccine appears to be effective in preventing severe symptoms of this illness.
• Wash your hands thoroughly. And make sure your children do, too. If your children are older, teach them to wash their hands, especially after using the toilet. It’s best to use warm water and soap and to rub hands vigorously for at least 20 seconds, remembering to wash around cuticles, beneath fingernails and in the creases of the hands. Then rinse thoroughly. Carry sanitizing wipes and hand sanitizer for times when soap and water aren’t available.
• Use separate personal items around your home. Avoid sharing eating utensils, drinking glasses and plates. Use separate towels in the bathroom.
• Keep your distance. Avoid close contact with anyone who has the virus, if possible.
• Disinfect hard surfaces. If someone in your home has viral gastroenteritis, disinfect hard surfaces, such as counters, faucets and doorknobs, with a mixture of 2 cups (0.47 liters) of bleach to 1 gallon (3.8 liters) of water.
• Check out your child care center. Make sure the center has separate rooms for changing diapers and preparing or serving food. The room with the diaper-changing table should have a sink as well as a sanitary way to dispose of diapers.

References