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Vomiting (Acute Gastroenteritis)

Overview

Acute gastroenteritis, often called “stomach flu,” is an inflammation of the stomach and intestines that typically presents with sudden onset vomiting, diarrhea, abdominal cramps, and sometimes fever. The condition is usually caused by an infection—viral, bacterial, or parasitic—but can also result from toxins, medication side‑effects, or food intolerances.

Who it affects: Everyone can develop acute gastroenteritis, but it is most common in children under five (who account for ~20 % of all outpatient visits for diarrhea in the U.S.) and in adults living in crowded or institutional settings such as nursing homes, schools, or military barracks.

Prevalence: According to the World Health Organization, there are an estimated 1.7 billion cases of diarrheal disease worldwide each year, and vomiting accompanies the illness in roughly 50‑70 % of cases. In the United States, the CDC reports ~179 million episodes of gastroenteritis annually, leading to ~200 000 hospitalizations and ~600 deaths, predominantly in the very young and the elderly.

Symptoms

Symptoms usually appear within hours to a few days after exposure to the causative agent and last 1‑3 days for most viral infections. The full symptom spectrum includes:

• Vomiting – sudden, forceful expulsion of stomach contents; may be non‑bilious or contain bile (greenish) if the stomach is empty.
• Diarrhea – loose, watery stools; may be accompanied by urgency.
• Abdominal pain or cramping – often colicky and centered around the lower abdomen.
• Fever – low‑grade (≤38 °C) is common; higher fevers suggest bacterial infection.
• Nausea – prior to vomiting, a feeling of queasiness.
• Headache – due to dehydration or fever.
• Loss of appetite – may be secondary to nausea.
• Fatigue and malaise – general sense of being unwell.
• Dehydration signs – dry mouth, decreased urine output, dizziness, sunken eyes, skin that stays tented when pinched.

Causes and Risk Factors

Infectious agents

• Viruses (most common) – Norovirus (≈50 % of outbreaks in the U.S.), Rotavirus (leading cause in children worldwide), Adenovirus, Astrovirus.
• Bacteria – Campylobacter jejuni, Salmonella, Escherichia coli (especially Shiga‑toxin producing strains), Shigella, Vibrio cholerae, Clostridioides difficile (often after antibiotics).
• Parasites – Giardia lamblia, Cryptosporidium, Entamoeba histolytica.

Non‑infectious triggers

• Food poisoning from toxins (e.g., Staphylococcus aureus, Bacillus cereus).
• Medication side‑effects (e.g., chemotherapy, opioids, antibiotics).
• Alcohol binge or excessive caffeine.
• Motion sickness, severe stress, or migraine.

Risk factors

• Age < 5 years or > 65 years.
• Close contact with an infected person (household, daycare, cruise ship).
• Travel to regions with poor sanitation.
• Immunocompromised state (HIV, chemotherapy, organ transplant).
• Recent use of antibiotics (risk for C. difficile).
• Poor hand hygiene or consumption of undercooked meat/seafood.

Diagnosis

Most cases of acute gastroenteritis are diagnosed clinically based on history and physical exam. Laboratory testing is reserved for severe, prolonged, or atypical presentations.

History & Physical Exam

• Onset, duration, and pattern of vomiting/diarrhea.
• Potential exposures (food, travel, sick contacts).
• Assess for dehydration (skin turgor, mucous membranes, orthostatic vitals).

Laboratory Tests

• Stool culture – identifies bacterial pathogens; ordered if diarrhea > 3 days, blood in stool, or high fever.
• Stool PCR panel – rapid detection of viral, bacterial, and parasitic DNA/RNA (e.g., BioFire FilmArray GI). Sensitivity > 90 %.
• Fecal leukocytes or calprotectin – markers of inflammatory (bacterial) infection.
• Blood work – CBC (leukocytosis suggests bacterial disease), electrolytes (to evaluate dehydration), renal function.
• C. difficile toxin assay – for patients with recent antibiotic exposure.

Imaging

Usually not required. Abdominal X‑ray or CT is considered only if there are red‑flag signs (e.g., perforation, obstruction, severe abdominal pain).

Treatment Options

The cornerstone of therapy is supportive care; most viral gastroenteritis resolves without specific antimicrobial treatment.

Rehydration

• Oral Rehydration Solutions (ORS) – contain a precise balance of glucose and electrolytes (e.g., WHO ORS, Pedialyte). Recommended for mild‑to‑moderate dehydration.
• IV Fluids – isotonic crystalloids (0.9 % saline or Lactated Ringer’s) for severe dehydration, inability to tolerate oral intake, or electrolyte derangements. Typical initial bolus: 20 mL/kg in children, 500–1000 mL in adults.

Dietary Measures

• Begin with clear liquids (broth, clear soups, diluted juice) once vomiting subsides.
• Progress to bland foods (BRAT diet – bananas, rice, applesauce, toast) after 24 h if tolerated.
• Avoid dairy, high‑fat, spicy, and high‑fiber foods until fully recovered.

Antiemetic Medications

• Ondansetron (Zofran) – 4 mg (children) or 4–8 mg (adults) orally or IV; shown to reduce vomiting and improve oral rehydration success in pediatric trials (NIH, 2020).
• Promethazine or Dexamethasone – sometimes used in adults, but sedation risk limits use.

Antidiarrheal Agents

• Loperamide – can be used for non‑inflammatory diarrhea in adults, but contraindicated in suspected bacterial dysentery or C. difficile infection.
• Avoid in children < 2 years.

Antibiotics

Reserved for specific bacterial pathogens:

• Campylobacter – azithromycin 500 mg daily for 3 days.
• Salmonella (invasive disease) – fluoroquinolone or ceftriaxone.
• Shigella – ciprofloxacin or azithromycin.
• C. difficile – oral vancomycin 125 mg q6h 10 days.

Routine antibiotics for viral gastroenteritis are ineffective and increase resistance.

Probiotics

Some meta‑analyses suggest that Lactobacillus rhamnosus GG or S. boulardii may shorten diarrhea duration by ~1 day, especially in children (Cleveland Clinic, 2022). Not a replacement for rehydration.

Living with Vomiting (Acute Gastroenteritis)

Daily Management Tips

• Hydration schedule: sip 5–10 mL every 5–10 minutes; aim for 1–2 L fluids per day for adults, more for children.
• Rest: limit physical activity; the body needs energy to fight infection.
• Temperature control: use a fan or light blanket; treat fever > 38.5 °C with acetaminophen (paracetamol) – avoid NSAIDs if dehydrated.
• Hygiene: wash hands with soap for ≥20 seconds after using the bathroom and before eating; disinfect contaminated surfaces with bleach solution (1 part bleach to 9 parts water).
• Monitoring: track number of vomiting episodes, stool consistency (Bristol Stool Chart), urine output (aim for ≥ 0.5 mL/kg/h).
• Medication timing: give antiemetics early (at first sign of vomiting) to improve oral intake success.
• Return to work/school: wait until 24 h after symptoms stop and no fever to reduce transmission.

Prevention

• Hand hygiene: wash hands after bathroom use, before preparing food, and after caring for a sick person.
• Food safety: cook meats to safe internal temperatures (e.g., poultry 165 °F/74 °C), wash fruits/vegetables, avoid unpasteurized dairy.
• Water safety: drink bottled or properly treated water when traveling; use chlorine tablets or filters when needed.
• Vaccination: Rotavirus vaccine (2‑dose series for infants) reduces severe gastroenteritis by up to 85 % (CDC, 2023). Consider hepatitis A vaccine for travelers to endemic areas.
• Surface disinfection: clean kitchen counters, bathroom fixtures, and high‑touch objects with EPA‑approved disinfectants during outbreaks.
• Avoid sharing utensils or personal items with an ill person.

Complications

While most cases resolve without lasting effects, untreated or severe gastroenteritis can lead to:

• Dehydration – electrolyte imbalances (hyponatremia, hypokalemia) that may cause seizures or cardiac arrhythmias.
• Acute kidney injury – especially in the elderly or those with pre‑existing renal disease.
• Gastrointestinal bleeding – from erosive gastritis or bacterial toxins.
• Septicemia – rare, but possible with invasive bacterial pathogens (e.g., Salmonella Typhi).
• Chronic post‑infectious irritable bowel syndrome (IBS) – occurs in up to 10 % of adults after severe gastroenteritis (NIH, 2021).
• Malnutrition – prolonged vomiting/diarrhea can impair nutrient absorption, especially in infants.

When to Seek Emergency Care

Prompt medical attention can prevent serious complications and ensure appropriate rehydration and treatment.

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Sources: Mayo Clinic, CDC, NIH, WHO, Cleveland Clinic, peer‑reviewed journals (JAMA, Lancet Infectious Diseases). All information reflects guidelines up to May 2026.

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