Gastroenteritis

Gastroenteritis is an inflammation of the mucous membrane of the stomach, small intestine and large intestine. In most cases, it is an infectious disease, although gastroenteritis can develop after taking medications and chemical toxic substances (e.g. metals, industrial substances).

Symptoms of gastroenteritis include anorexia, nausea, vomiting, diarrhea, and abdominal discomfort. Diagnosis is by clinical and bacteriologic examination of stool, although immunologic testing is increasingly used. Treatment of gastroenteritis is symptomatic, but parasitic and some bacterial infections require specific antibacterial therapy.

Gastroenteritis is usually uncomfortable but may resolve without treatment. The loss of electrolytes and fluids from gastroenteritis is of little more than a minor concern for a healthy middle-aged person, but can be quite severe for children and adolescents, the elderly, or people with serious underlying medical conditions. Worldwide, approximately 3-6 million children die from infectious gastroenteritis each year.

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What causes gastroenteritis?

Infectious gastroenteritis can be caused by viruses, bacteria, or parasites.

Viruses

Viruses are the most common cause of gastroenteritis in the United States. They infect the enterocytes of the villous epithelium of the small intestine. The result is transudation of fluid and salts into the intestinal lumen; sometimes carbohydrate malabsorption worsens symptoms, causing osmotic diarrhea. The diarrhea is watery. The most common type is inflammatory (exudative) diarrhea, with white blood cells and red blood cells or even significant amounts of blood in the stool. Four categories of viruses cause most gastroenteritis: rotavirus, caliciviruses [which include norovirus (formerly called Norwalk virus)], astrovirus, and enteric adenovirus.

Rotavirus is the most common cause of sporadic, severe cases of dehydration diarrhea in young children (peak incidence in children 3-15 months). Rotavirus is highly contagious; most infections occur via the fecal-oral route. Adults may become infected after close contact with an infected infant. In adults, the disease is mild. Incubation is 1-3 days. In temperate climates, most infections occur in the winter. Each year in the United States, a wave of rotavirus cases begins in November in the Southwest and ends in the Northeast in March.

Caliciviruses typically affect adolescents and adults. Infection occurs year-round. Caliciviruses are the main cause of sporadic viral gastroenteritis in adults and epidemic viral gastroenteritis in all age groups; infection usually occurs through water or food. Human-to-human transmission is also possible, as the virus is highly contagious. Incubation is 24-48 hours.

Astrovirus can infect people of any age, but usually affects infants and small children. Infection usually occurs in winter. Transmission occurs via the fecal-oral route. Incubation is 3-4 days.

Adenoviruses are the 4th, but most common cause of viral gastroenteritis in children. Infection occurs year-round, with a slight increase in summer. Children under 2 years of age are primarily at risk of infection. Transmission occurs by the feco-oral route. Incubation is 3-10 days.

In people with immunodeficiency, gastroenteritis may be caused by other viruses (eg, cytomegalovirus, enterovirus).

Bacteria

Bacterial gastroenteritis is less common than viral gastroenteritis. Bacteria cause gastroenteritis by several mechanisms. Certain species (eg, Vibrio cholerae, enterotoxigenic strains of Escherichia coli ) reside within the intestinal mucosa and secrete enterotoxins. These toxins interfere with intestinal absorption, causing secretion of electrolytes and water by stimulating adenylate cyclase, resulting in watery diarrhea. Clostridium difficile produces a similar toxin, which results from overgrowth of the microflora after antibiotic use.

Some bacteria (e.g., Staphylococcus aureus, Bacillus cereus, Clostridium perfringens) produce an exotoxin that is ingested when contaminated food is consumed. The exotoxin can cause gastroenteritis without a bacterial infection. These toxins typically cause acute nausea, vomiting, and diarrhea within 12 hours of ingestion of contaminated food. Symptoms of gastroenteritis resolve within 36 hours.

Other bacteria (e.g., Shigella, Salmonella, Campylobacter, some strains of E. coli) penetrate the mucous membrane of the small intestine or colon and cause microscopic ulcers, bleeding, exudation of protein-rich fluid, secretion of electrolytes and water. The invasion process may be accompanied by the synthesis of enterotoxin by the microorganisms. In such diarrhea, the feces contain leukocytes and erythrocytes, sometimes with a large amount of blood.

Salmonella and Campylobacter are the most common causes of bacterial diarrhea in the United States. Both infections are usually acquired through poorly handled poultry; sources include unpasteurized milk, undercooked eggs, and contact with reptiles. Campylobacter is sometimes transmitted from dogs or cats with diarrhea. Shigella species are the third leading cause of bacterial diarrhea in the United States and are usually transmitted from person to person, although foodborne outbreaks have occurred. Shigella dysenteriae type 1 (not found in the United States) produces Shiga toxin, which can cause hemolytic uremic syndrome.

Diarrhea can be caused by some subtypes of E coli. Epidemiology and clinical manifestations vary depending on the subtype.

1. Enterohemorrhagic E coli is the most clinically important subtype in the United States. The bacterium produces Shiga toxin, which causes bloody diarrhea. E coli 0157:H7 is the most common strain of this subtype in the United States. Undercooked ground beef, unpasteurized milk and juice, and contaminated water are possible sources of transmission. Person-to-person transmission is most common in patient care settings. Hemolytic uremic syndrome is a severe complication that occurs in 2-7% of cases, usually in children and the elderly.
2. Enterotoxic E coli produces two types of toxin (one similar to cholera toxin) that cause watery diarrhea. This subtype is the leading cause of traveler's diarrhea.
3. Enteropathogenic E coli causes watery diarrhea. The subtype was once a major cause of diarrhea outbreaks in child care facilities, but is now rare. (4) Enteroinvasive E coli is most common in developing countries and causes bloody or non-bloody diarrhea. Isolated cases have been reported in the United States.

Several other bacteria cause gastroenteritis, but they are rare in the United States. Yersinia enterocolitica can cause gastroenteritis or a syndrome resembling appendicitis. Infection occurs through undercooked pork, unpasteurized milk, or water. Some species of Vibrio (eg, V. parahaemolyticus) cause diarrhea after eating undercooked seafood. V. cholerae occasionally causes severe dehydrating diarrhea in developing countries. Listeria causes gastroenteritis after eating contaminated food. Aeromonas infects the body through swimming or drinking contaminated water. Plesiomonas shigelloides can cause diarrhea in patients who have eaten raw shellfish or traveled to tropical areas of developing countries.

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Parasites

Certain intestinal parasites, especially Giardia lamblia, attach to and burrow into the intestinal lining, causing nausea, vomiting, diarrhea, and general malaise. Giardiasis occurs throughout the United States and around the world. The infection can be chronic and cause malabsorption syndrome. Transmission is usually person-to-person (often in day care centers) or contaminated water.

Cryptosporidium parvum causes watery diarrhea, sometimes accompanied by abdominal cramps, nausea, and vomiting. In healthy individuals, the illness may be self-limiting and lasts about 2 weeks. In immunocompromised patients, the illness may be severe, causing significant electrolyte and fluid losses. Cryptosporidium is usually acquired through contaminated water.

There are parasite species including Cyclospora cayetanensis, Isospora belli, and some microsporidia (e.g., Enterocytozoon bieneusi, Encephalitozoon intesfmalis) that can cause symptoms similar to those of cryptosporidiosis, especially in immunocompromised patients. Entamoeba histolytica (amebiasis) is a major cause of subacute bloody diarrhea in developing countries, and is occasionally diagnosed in the United States.

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Symptoms of gastroenteritis

The nature, severity, and symptoms of gastroenteritis vary. In general, gastroenteritis develops suddenly, with anorexia, nausea, vomiting, borborygmi, abdominal cramps, and diarrhea (with or without blood and mucus). Malaise, myalgia, and severe weakness sometimes occur. The abdomen may be distended and tender to palpation; in severe cases, muscle tension may be present. Gas-distended intestinal loops may be palpated. Abdominal borborygmi may occur without diarrhea (an important distinguishing feature from paralytic ileus). Persistent vomiting and diarrhea may lead to intravascular fluid loss with hypotension and tachycardia. In severe cases, shock with vascular insufficiency and oliguric renal failure may develop.

If vomiting is the primary cause of dehydration, metabolic alkalosis and hypochloremia develop. In case of severe diarrhea, acidosis may develop. Both vomiting and diarrhea may cause hypokalemia. If hypotonic solutions are used as replacement therapy, hyponatremia may develop.

In viral infections, watery diarrhea is the main symptom of gastroenteritis; the stool rarely contains mucus or blood. Gastroenteritis caused by rotavirus in infants and young children may last 5 to 7 days. Vomiting occurs in 90% of patients, and fever greater than 39 "C is observed in approximately 30%. Caliciviruses usually manifest themselves with an acute onset, vomiting, cramping abdominal pain and diarrhea lasting 1-2 days. In children, vomiting prevails over diarrhea, while in adults, diarrhea usually prevails. Patients may experience fever, headache and myalgia. The symptom of adenovirus gastroenteritis is diarrhea lasting 1-2 weeks. Infection in infants and children is accompanied by mild vomiting, which usually begins 1-2 days after the onset of diarrhea. Low fever is observed in approximately 50% of patients. Astrovirus causes a syndrome similar to mild rotavirus infection.

Bacteria that cause invasive disease (e.g., Shigella, Salmonella) typically cause fever, severe weakness, and bloody diarrhea. Bacteria that produce enterotoxin (e.g., S. aureus, B. cereus, C. perfringens) typically cause watery diarrhea.

Parasitic infections are usually accompanied by subacute or chronic diarrhea. In most cases, the stool is not bloody; an exception is E. histolytica, which causes amoebic dysentery. Malaise and weight loss are characteristic if diarrhea is persistent.

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Diagnosis of gastroenteritis

Other GI disorders that cause similar symptoms (eg, appendicitis, cholecystitis, ulcerative colitis) should be excluded. Findings that suggest gastroenteritis include profuse watery diarrhea; history of ingestion of potentially contaminated food (especially during an established outbreak), contaminated water, or known GI irritants; recent travel; or contact with suspected cases. E. coli 0157:1-17, which causes diarrhea, is notorious for being more hemorrhagic than infectious, with symptoms of GI bleeding and little or no bloody stool. Hemolytic uremic syndrome may result from renal failure and hemolytic anemia. A history of oral antibiotic use (within 3 months) should raise additional suspicion for C. difficile infection. Acute abdomen is unlikely in the absence of abdominal tenderness and localized tenderness.

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Stool studies

If occult blood is detected on rectal examination or if watery diarrhea persists for more than 48 hours, stool testing for occult blood and stool testing (red blood cells in stool, eggs, parasites) and culture are indicated. However, stool antigen detection by enzyme immunoassay is more sensitive for diagnosing giardiasis or cryptosporidiosis. Kits can diagnose rotavirus and enteric adenovirus infections by detecting viral antigen in stool, but these tests are usually performed only when an outbreak has been documented.

All patients with bloody diarrhea should be tested for E. coli 0157:1-17, as should patients with nonbloody diarrhea in a known outbreak. Specific cultures should be obtained, since this organism is not detected by routine culture. Alternatively, urgent ELISA testing for Shiga toxin in stool may be performed; a positive test indicates infection with E. coli 0157:1-17 or one of the other serotypes of enterohemorrhagic E. coli. (Note: Shigella species in the United States do not secrete Shiga toxin.)

Adults with severe bloody diarrhea should have a sigmoidoscopy with culture and biopsy. Colonic mucosal findings may aid in the diagnosis of amoebic dysentery, shigellosis, and £ coli 0157:1-17 infection, although ulcerative colitis may have similar findings. Patients who have recently taken antibiotics should have a stool sample tested for C. difficile toxin.

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General tests

Serum electrolytes, blood urea nitrogen, and creatinine should be measured in critically ill patients to assess hydration and acid-base status. Complete blood count ( CBC) values are nonspecific, although eosinophilia may indicate parasitic infection.

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Treatment of gastroenteritis

Supportive care for gastroenteritis is all that is needed for most patients.

Bed rest with easy access to a toilet or bedpan is recommended. Oral glucose-electrolyte solution, liquid food, or broth prevents dehydration and is used as a treatment for moderate dehydration. Even if the patient is vomiting, these fluids should be sipped; vomiting may decrease as dehydration decreases. Children develop dehydration more rapidly, so appropriate reparative solutions (some are commercially available) should be given. Carbonated drinks and sports drinks have an inadequate glucose-to-Na ratio and are therefore not recommended for children under 5 years of age. If the child is breast-fed, breastfeeding should be continued. If vomiting is prolonged or severe dehydration develops, intravenous volume expansion and electrolyte replacement are indicated.

If there is no vomiting, the patient tolerates fluid intake well and appetite appears, you can gradually begin to eat. There is no need to limit the diet to only light food (white bread, semolina porridge, gelatin, bananas, toast). Some patients may experience temporary lactose intolerance.

Antidiarrheals are safe in patients 5 years or older with watery diarrhea (as evidenced by heme-negative stools). However, antidiarrheals may worsen the condition in patients with C. difficile or E. coli 0157:1-17 infection and should not be given to patients who have received antibiotics or who have heme-positive stools without a clear diagnosis. Effective antidiarrheals include loperamide 4 mg orally initially, followed by 2 mg orally with each episode of diarrhea (maximum 6 doses/day, or 16 mg/day); diphenoxylate 2.5 to 5 mg 3 to 4 times daily in tablet or liquid form; or bismuth subsalicylate 524 mg (two tablets or 30 mL) orally every 6 to 8 hours daily.

In severe vomiting and if surgical pathology has been excluded, antiemetics may be effective. Drugs used in adults include prochlorperazine 5-10 mg intravenously 3-4 times a day or 25 mg rectally 2 times a day; and promethazine 12.5-25 mg intramuscularly 2-3 times a day or 25-50 mg rectally. These drugs should be avoided in children because of their insufficient evidence of efficacy and a high tendency to develop dystonic reactions.

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Antibacterial drugs for gastroenteritis

Empirical antibiotics are generally not recommended except in some cases of traveler's diarrhea or if there is a high suspicion of Shigella or Campylobacter infection (eg, contact with a known carrier). Otherwise, antibiotics should await stool culture results, particularly in children, who have a higher incidence of E. coli 0157:1-17 infection (antibiotics increase the risk of hemolytic uremic syndrome in patients infected with E. coli 0157:1-17).

Antibiotics are not always indicated in proven bacterial gastroenteritis. They are ineffective against Salmonella infection and prolong stool fluid loss. Exceptions include immunocompromised patients, neonates, and patients with Salmonella bacteremia. Antibiotics are also ineffective against toxic gastroenteritis (e.g., S. aureus, B. cereus, C. perfringens). Indiscriminate use of antibiotics contributes to the emergence of drug-resistant strains of microorganisms. However, certain infections do require antibiotics.

The use of probiotics such as lactobacilli is generally safe and may be effective in reducing symptoms of gastroenteritis. They can be taken in the form of yogurt with active culture.

For cryptosporidiosis in immunocompromised children, nitazoxanide may be effective. The dose is 100 mg orally twice daily for children 12–47 months and 200 mg orally twice daily for children 4–11 years.

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How to prevent gastroenteritis?

Gastroenteritis is difficult to prevent because of the asymptomatic nature of the infection and the ease with which many pathogens, especially viruses, are transmitted from person to person. In general, appropriate preventive measures should be taken when interacting with and preparing food. Travelers should avoid consuming potentially contaminated food and drink.

Breastfeeding provides some protection for neonates and infants. Caregivers should wash their hands with soap and water after each diaper change, and the work area should be disinfected with a freshly prepared 1:64 solution of household disinfectant (1/4 cup diluted in 1 gallon of water). Children with diarrhea should be excluded from the day care facility until symptoms resolve. Children infected with enterohemorrhagic strains of E. coli or Shigella should have two negative stool cultures before being allowed to attend.

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