Gastroenteritis: When Vomiting and Diarrhea Become Dangerous

Understanding the Cause

Viral gastroenteritis — most cases. Norovirus, Rotavirus, Astrovirus. No antibiotic treatment. Resolves in 24-72 hours with supportive care.

Bacterial gastroenteritis — less common but potentially more serious:

• Salmonella: contaminated eggs, poultry, unpasteurized products. Watery to bloody diarrhea, fever 12-24 hours after exposure.
• Campylobacter: undercooked poultry, raw milk. Bloody diarrhea, cramping, fever. Most common bacterial cause in the US.
• Shigella (dysentery): fecal-oral transmission, minimal infective dose. Bloody diarrhea, high fever, tenesmus (constant urge to defecate).
• E. coli O157:H7: undercooked beef, contaminated produce. Bloody diarrhea without fever. Risk of hemolytic uremic syndrome (HUS — kidney failure and anemia) — particularly dangerous in children.
• Staphylococcal toxin: mayonnaise, dairy, room-temperature foods. Rapid onset (1-4 hours), primarily vomiting rather than diarrhea. No antibiotic needed — self-limited toxin effect.
• Clostridium perfringens: improperly held meat and poultry. Watery diarrhea 8-16 hours after exposure. Self-limited.

Protozoal gastroenteritis:

• Giardia: contaminated water. Chronic watery diarrhea, flatulence, nausea. Treatment: metronidazole 250mg 3x/day × 5-7 days.
• Cryptosporidium: water contamination. Self-limited in healthy adults; severe in immunocompromised. No reliable antibiotic.

Hydration — The Priority

Most gastroenteritis deaths occur from dehydration. The treatment is ORS (oral rehydration solution), given consistently.

Adult ORS administration:

• Sip small amounts continuously rather than drinking large volumes that trigger vomiting
• 200-400ml ORS per episode of diarrhea or vomiting (WHO guideline)
• Clear broths, diluted sports drinks, and similar fluids are acceptable substitutes when ORS is unavailable
• Do not give full-strength sports drinks — the sugar content is too high and can worsen osmotic diarrhea

The rule for ongoing losses:

• Per loose stool: 200-400ml ORS
• Per vomiting episode: 100-200ml ORS

If the patient can keep small sips down, continue. Even if some vomiting occurs, some fluid is being absorbed.

When oral route fails:

• If the patient cannot keep anything down for 4-6 hours, IV access and IV fluids are needed
• Alternative: rectal fluid administration (proctoclysis) — slowly infusing ORS rectally via a soft tube works for hydration in patients who cannot tolerate oral intake (not practical in most field settings)

Medications

Loperamide (Imodium)

Dose: 4mg initial dose, then 2mg after each loose stool. Maximum 16mg/day.

Use for:

• Uncomplicated watery diarrhea without blood or high fever
• Traveler's diarrhea
• Viral gastroenteritis where reducing stool frequency improves hydration capacity

Do NOT use for:

• Bloody diarrhea (dysentery)
• Fever > 38.5°C
• Suspected C. difficile infection (antibiotic-associated diarrhea, especially after clindamycin use)
• Children under 2 years

Bismuth Subsalicylate (Pepto-Bismol)

Has mild antimicrobial activity and anti-secretory effects. Reduces diarrhea frequency and duration modestly. Safe for most adults. Two tablets every 30-60 minutes as needed (maximum 8 doses/day). Turns stool black — reassure the patient.

Antiemetics

For vomiting preventing adequate hydration:

• Ondansetron (Zofran) 4mg orally or under the tongue — fastest, most effective option
• Promethazine (Phenergan) 12.5-25mg — also antihistamine, causes sedation
• Metoclopramide 10mg — prokinetic, improves gastric emptying

Antibiotics: When Indicated

Antibiotics for gastroenteritis are appropriate in specific situations:

Antibiotic-indicated:

• Moderate-severe traveler's diarrhea (> 3 loose stools/day with at least one associated symptom: nausea, vomiting, cramps, blood, fever): azithromycin 1g single dose or 500mg/day × 3 days; or ciprofloxacin 500mg twice daily × 1-3 days
• Dysentery (bloody diarrhea with fever): ciprofloxacin 500mg twice daily × 3-5 days
• Shigella: azithromycin 500mg/day × 3 days or ciprofloxacin
• Salmonella with fever and systemic symptoms (not uncomplicated self-limited Salmonella): ciprofloxacin 500mg twice daily × 7 days
• Giardia: metronidazole 250mg 3x/day × 5-7 days

Antibiotics NOT indicated for:

• Uncomplicated viral gastroenteritis (most cases)
• E. coli O157:H7 (bloody diarrhea without fever): antibiotics may increase risk of HUS — do not treat
• C. perfringens or Staphylococcal toxin (food poisoning without fever): self-limited
• Any watery diarrhea without fever or bloody stool in otherwise healthy adult

Dietary Management

What to Eat

The BRAT diet (Bananas, Rice, Applesauce, Toast): Traditional recommendation. Safe starting point. Provides bland, easily digested carbohydrates. Does not need to be strictly followed — any bland, low-fat food the patient can tolerate is appropriate.

Reintroduction timeline:

• 0-4 hours: ORS only
• 4-8 hours: clear broths, diluted juices, plain crackers
• 8-24 hours: BRAT foods, plain rice, boiled potatoes
• After 24 hours: gradual return to normal diet

Probiotics: Lactobacillus rhamnosus GG and Saccharomyces boulardii have modest evidence for reducing duration of acute viral gastroenteritis, particularly in children. If available, worth adding. 10-20 billion CFU daily.

Foods to Avoid

During acute illness:

• High-fat foods (slow gastric emptying, worsen nausea)
• High-sugar foods (osmotic effect can worsen secretory diarrhea)
• Dairy (secondary lactase deficiency after viral enteritis — temporary lactose intolerance)
• Caffeine (increases intestinal motility)
• Alcohol

When to Resume Normal Diet

Most people with viral gastroenteritis can resume near-normal eating within 24-48 hours. The old practice of extended "clear liquid" diets for days prolonged recovery by denying the gut the nutrients needed for mucosal repair.

Special Considerations

Food Safety in Field Settings

Gastroenteritis in a group is often preventable through food handling practices. The most common field causes:

• Cross-contamination: meat juices contaminating ready-to-eat foods
• Temperature abuse: foods held at 40-140°F (4-60°C) for more than 2 hours allow bacterial multiplication
• Contaminated water: all water of uncertain quality should be treated before use
• Handwashing: fecal-oral transmission is the route for most gastrointestinal illness — hand hygiene before food handling and after toilet use prevents transmission

If multiple group members develop gastroenteritis simultaneously (same incubation time, same symptoms), identify the common food source and remove it.

Norovirus Decontamination

Norovirus is extraordinarily contagious — fewer than 10 viral particles cause infection. Standard hand sanitizer (alcohol-based) does NOT kill Norovirus. Hand washing with soap and water for 20 seconds is required. Surfaces require bleach solution (1 tablespoon bleach per quart of water) for decontamination.

In a group setting with a Norovirus outbreak: isolate the ill, use dedicated bathroom facilities if possible, and stringent handwashing protocols.