Gastroenteritis

Definitions
Gastroenteritis is a nonspecific term for various pathologic states of the gastrointestinal tract. The primary manifestation is diarrhea, but it may be accompanied by nausea, vomiting, and abdominal pain

Pathophysiology
Infectious agents usually cause acute gastroenteritis. These agents cause diarrhea by adherence, mucosal invasion, enterotoxin production, and/or cytotoxin production. Mechanism:

• Osmotic, due to an increase in the osmotic load presented to the intestinal lumen, either through excessive intake or diminished absorption
• Inflammatory (or mucosal), when the mucosal lining of the intestine is inflamed
• Secretory, when increased secretory activity occurs
• Motile, caused by intestinal motility disorders

Epidemiology
3-5 billion cases/year,-lleading cause of death in many underdeveloped countries. Approximately 30-50% of visitors to developing countries develop, and perhaps return with, diarrhea.
Nursing home outbreaks have significant mortality.
Day care center and prison outbreaks have occurred.
Salmonella outbreaks in 2008 from Mexican hot peppers and tomatoes, peanuts, and Honduran cantaloupes
Bacterial: Poor reporting overall; ~6 million cases per year:

• In the US, Salmonella, Campylobacter jejuni, Shigella, Clostridium perfringens, and Staphylococcus aureus account for 90% of the cases, totaling ~45,000 hospitalizations and 2,700 deaths per year. In Europe, Campylobacter jejuni and Salmonella make up 95% of cases
• Campylobacter, Cryptosporidium, Listeria, Salmonella, Shigella are, in order, the most common among children less than 4 years old
• Approximate incidence of foodborne diarrhea is 1 in 4 people per year; however, only 1/10 of those, approximately 2,500/100,000 people per year, acquire bacterial food poisoning

Aetiology

Viral (50-70%)	Norovirus, calicivirus, rotavirus, adenovirus, parvovirus, astrovirus, coronavirus
Bacterial (15-20%)	Shigella, Salmonella, C jejuni, Yersinia enterocolitica, E coli - (Enterohemorrhagic O157:H7, enterotoxigenic, enteroadherent, enteroinvasive), V cholera, Aeromonas, C difficile, Clostridium perfringens, Listeria
Parasitic (10-15%)	Giardia. Amebiasis, Cryptosporidium, Cyclospora
Food-borne toxigenic diarrhea	Preformed toxin -S aureus, B cereus Postcolonization -V cholera, C perfringens, enterotoxigenic E coli, Aeromonas
Shellfish poisoning	Paralytic shellfish poisoning (PSP) - Saxitoxin Neurologic shellfish poisoning (NSP) - Brevetoxin Diarrheal shellfish poisoning (DSP) - Okadaic acid
Drug-associated diarrhea	Antibiotics, (due to alteration of normal flora), Laxatives,. Colchicine, Quinidine, Cholinergics
Pseudomembranous colitis	C difficile
Other causes	Unknown agents(especially in developing countries), Ischemic colitis, Ulcerative colitis, Crohn disease, Carcinoid tumor or vasoactive intestinal peptide tumor (VIPoma), AIDS, Dumping or short bowel syndrome,Radiation or chemotherapy

Presentation
The condition is usually of acute onset, normally lasting 1–6 days, and is self-limiting.

• Nausea and vomiting
• Diarrhea- daily stools with a mass greater than 15 g/kg for children younger than 2 years and greater than 200 g for children aged 2 years and older. Adult stool patterns vary from 1 stool every 3 days to 3 stools per day; therefore, consider individual stool patterns.
• Loss of appetite
• Fever
• Headaches
• Abnormal flatulence
• Abdominal pain
• Abdominal cramps
• Bloody stools (dysentery - suggesting infection by amoeba,Campylobacter, Salmonella, Shigella or some pathogenic strains of Escherichia coli[4])
• Fainting and Weakness
• Heartburn

Investigation

Stool culture	Blood agar - All aerobic bacteria and yeast; detects cytochrome oxidase production MacConkey EMB agar - Inhibits gram-positive organisms; permits lactose fermentation XLD agar and HE agar - Inhibit gram-positive organisms and nonpathogenic gram-negative bacilli; permit lactose fermentation and H2S production Skirrow agar - Selective for Campylobacter species SM agar - Selective for enterohemorrhagic E coli CIN agar - Selective for Y enterocolitica Thiosulfate-citrate-bile-sucrose agar - Selective for Vibrio species CCFE agar - Selective for C difficile
Electrolytes and BUN tests	rule out hyponatremia or hypernatremia
Enzyme-linked immunosorbent assay
Abdominal series	only when bowel obstruction, toxic megacolon, or perforation is suspected.
Sigmoidoscopy	if pseudomembranous colitis or inflammatory bowel disease is suspected.

Management

Emergency Management	Rehydrate orally or intravenously as needed. Treat symptoms (eg, fever, pain) as indicated. Identify complications. Prevent the spread of infections. Identify public health concerns and treat certain specific cases with specific or empiric antibiotic therapy.
Rehydration	1-2 L dextrose 5% in 0.5 isotonic sodium chloride solution with 50 mEq NaHCO3and 10-20 mEq KCl over 30-45 minutes may be necessary in patients who are severely dehydrated. Indications :severe intractable vomiting, altered consciousness, severe dehydration, ileus, excessive choleralike stools, and time or environment not conducive to oral rehydration therapy (
Antiemetics	eg. prochloperazine 12.5mg/6h IM
Antidiarrheals (antimotility agents)	bismuth subsalicylate (Pepto-Bismol). For patients older than 14 years, give 2 tablets or 20 mL PO q30min (not recommended in children)
Antibiotics	indicated if systematically unwell, immunosuppressed or elderly - Cholera: tetracycline reduces transmission - Salmonella: ciprofloxacin 500mg/12h PO, 200-400mg.12h IVI over 60 min - Shigella & Campilobacter: ciprofloxacin as above
Consultation with infectious disease specialist.	patients with chronic diarrhea, patients whose conditions have parasitic etiologies, patients infected with C difficile when vancomycin use is contemplated, patients who relapse, and patients with AIDS who have diarrhea.
Follow-up	if diarrhea persists longer than 10 days.

Complications
Dehydration
Malabsorption
Transient lactose intolerance
Chronic diarrhea
Systemic infection (meningitis, arthritis, pneumonia) especially with Salmonella infections
Sepsis (Salmonella, Yersinia, Campylobacter organisms)
Hemolytic-uremic syndrome (much more common in children, especially with E coli O157:H7)
Toxic megacolon
Reactive arthritides (Salmonella, Shigella, Yersinia, Campylobacter, Giardia organisms)
Persistent diarrhea
Thrombotic thrombocytopenic purpura or TTP (E coli O157:H7)
Guillain-Barré syndrome (Campylobacter organisms)

Prognosis
Most cases of gastroenteritis are self-limited with an excellent prognosis.