Episode 36 – Diagnosis and Management of Acute Gastroenteritis in the Emergency Department

Acute Gastroenteritis- Author: Dr. Brian Geyer


  • Do both vomiting and diarrhea have to be present? No
    • 1996 AAP guidelines, 2016 ACG guidelines, and 2017 IDSA guidelines all note diarrhea illness but may be vomiting predominant.
  • Studies use more vague definitions like:
    • > 1 episode of vomiting and/or > 3 episodes of diarrhea in 24 hours without known chronic cause like inflammatory bowel disease.
    • Diarrhea is at least 3 unformed stools per day.
    • Acute episode <14 days
    • Persistent episode 14-29 days
    • Chronic diarrhea >29 days
  • Patients in the ED may present with only some of these symptoms depending their time in course of illness.

Literature Review:

  • There is abundant literature on pediatric AGE but sparse research on AGE in adults. Therefore, many recommendations are extrapolated from the pediatric literature.


  • 70% of US cases are estimated to be caused by viruses, norovirus being most common.
    • o 26% norovirus
    • o 18% rotavirus
  • Among bacterial causes:
    • o 5.3% Salmonella, most common
    • o 5.3% Clostridium
    • o 3% Campylobacter
    • o 3% parasitic infections
  • Large portion, 51%, have no cause identified. (In ED patients)
  • Interestingly, 79% of cases never have a cause identified (not ED specific)
  • In ED patients, only 25% ever have a cause identified, this increases to 49% when a stool sample is obtained. (not ED specific)
  • Food poisoning is responsible for 5% of AGE but results in 30% of deaths. Most commonly:
    • Salmonella, Clostridium perfringens, and Campylobacter
    • Majority of foodborne illness is still viral, mostly norovirus
  • E Coli is normal in the gut, but two most common causes are:
    • Shiga toxin Ecoli (STEC) AKA enterohemorrhagic Ecoli (EHEC) – causes Hemolytic Uremic Syndrome in 5-10%
    • Entertoxigenic Ecoli (ETEC) – causes traveler’s diarrhea
    • Both cause self-limited illness.

Alternate Diagnoses:

  • Appendicitis: In the peds literature, misdiagnosis of appendicitis as AGE leads to 47% absolute increased risk of perforation. Suggestive findings include:
    • Migration of pain to RLQ
    • RLQ tenderness on exam (initial or repeat)
    • Absence of diarrhea
    • Pain not improved with episodes of diarrhea
    • Negative factors include multiple ill family members, recent international travel, presence of diarrhea (as defined above).
  • Ciguatera Fish Poisoning
    • Toxin produced by algae consumed by reef fish like grouper, red snapper, sea bass and Spanish mackerel.
    • Symptoms begin 6-24 hours post ingestion.
    • Fish tastes normal.
    • Patients may develop neurological symptoms like paresthesias, generalized pruritis, and reversal of hot/cold sensation.
    • Symptoms resolve spontaneously, and treatment with mannitol is controversial.
  • Scombroid Poisoning
    • Ingesting fish in the Scombroidae family – mackerel, bonito, albacore, and skipjack – that have been stored improperly
    • Bacteria produce histidine decarboxylase which converts histidine to histamine
    • Causes abdominal cramps and diarrhea, and may cause metallic bitter or peppery taste in mouth, and facial flushing within 20-30 min of ingestion
    • Can be confused with allergic reaction
    • Symptoms resolve in 6-8 hours
    • Notification of health dept may prevent others from being infected.
  • Page 5 Table 1- Distinguishing Factors in the Differential Diagnosis of AGE


  • Table 2, page 6 has key questions to ask.
  • Onset, timing, number of stools, presence of blood, fever, quality of abdominal pain and location, recent antibiotics, etc.
  • Extremes of age, immunosuppression, and pregnancy should be identified. Mortality is highest in the patients >65 yo.

Physical Exam:

  • We talked about RLQ abd pain, but what about bloody stool?
  • An observational study of 889 adults and 151 pediatric with AGE showed that a negative fecal occult test showed accurately excluded invasive bacterial etiology with a NPV 87% in adults and 96% in children. But PPV was only 24%.

Laboratory Testing and Imaging:

  • Dehydration is the biggest contributor to mortality, especially in the very young and elderly.
  • Lab evaluation for dehydration is recommended in these populations.
  • No consistent association between lab abnormalities and bacterial etiology.
  • WBC and differential does not differentiate bacterial vs viral, but may help in identifying severity of illness.
  • Hemoglobin and platelets are helpful if HUS is suspected.
  • Stool Cultures:
    • 2017 IDSA guidelines recommends them in patients with fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis, noting these patients are at higher risk of bacterial infection. Specifically, Salmonella, shigella, Campylobacter, and Yersinia
    • 2016 ACG guidelines recommend them for patients with watery diarrhea and moderate to severe illness with fever for at least 72 hours.
    • Consider them for immunocompromised patients and those with recent abx use or hospitalization.
  • C Difficile testing is recommended for all patients with AGE who are age >2 with a history of recent abx use or recent hospitalization
  • Blood cultures are recommended for patients <3 months old and any patient with signs of sepsis.
  • Imaging is generally plain film to exclude free air of surgical abdomen, or CT with contrast to evaluate for complications of AGE like aortitis, mycotic aneurysm, toxic megacolon, abscess, or perforation.


  • Oral rehydration is preferred. Oral rehydration solutions in patients tolerating oral fluids.
    • ORS packets
    • Pedialyte, Hydralyte, etc
    • Sports drinks are safe but have less potassium. Higher sugar solutions can be diluted 50%
    • Coconut water
    • Half strength apple juice has been studied in pediatrics and decreased treatment failure.
  • IV hydration for patients with severe dehydration, hypovolemic shock, septic shock, or failed oral rehydration.
  • Don’t forget to replace electrolytes if giving IV hydration.


  • Ondansetron (Zofran) reduces need for IV hydration in peds. (0.15mg/kg oral liquid) but doesn’t reduce hospitalizations or return visits (low numbers)
  • No benefit to higher dose ondansetron.
  • IV ondansetron vs metoclopramide performance is similar in peds.
  • No benefit in studies to giving dexamethasone, or dimenhydrinate (dramamine)
  • Proshlorperazine 10mg IV was shown to be superior to promethazine 25mg IV for symptom relief in adults, with less sedation
  • No suggestions regarding medication choice from guidelines.
  • Sniffing isopropyl alcohol soaked pads twice q 2min was shown superior vs placebo in controlling nausea, but effect is gone at 30 minutes.
  • Ginger is reported to be helpful at 250mg QID in pregnant patients and post op patient. No data in AGE.
  • Loperamide is recommended as an adjunct to abx by the ACG. Risk is too high in patients <3 yo and 3-12 with moderate dehydration, blood stool, or severe disease.
  • Loperamide is also contraindicated if STEC is suspected, due to increased development of HUS
  • Probiotics may reduce diarrhea by one day.
  • World Health Organization recommends zinc supplements for children with diarrhea. In the US only recommended to reduce duration in severely malnourished children age 6mos-5yo.


  • Patients with traveler’s diarrhea from Latin America, Caribbean, and Africa will improve faster with abx therapy. Azithromycin 1gm PO x 1, Cipro 750 mg PO x 1, or Cipro 500mg PO BID x 3 days.
  • Patients with traveler’s diarrhea from South Asia and Southeast Asia have increased strains of fluoroquinolone resistant Campylobacter. Aizthromycin 1gm PO x 1 or 500mg PO daily for 3 days is recommended.
  • Great chart Table 4, page 12, on abx recommendations.
  • Shellfish ingestion – Doxy, Azithomycin, or Cipro.
  • C Diff – first line is oral vancomycin 125 mg PO QID for 10 days or Fidaxomicin 200mg PO BID for 10 days. Metronidazole is less effective due to resistance and is only used if the above is not available.
  • STEC should not be treated with abx due to increased HUS, neither should close contacts be prophylaxed with abx.
  • Hospitalized patients should be treated empirically pending stool studies.
  • Giardia is self-limited but can be treated with abx therapy.
  • Cryptosporidium is also self-limited but abx therapy is recommended for diarrhea >1-2 weeks, or immunocompromised patients.


  • No specific recommendations. Just prove patient is tolerating adequate oral fluids first.

Special Populations:

  • Immunocompromised (HIV/AIDS, etc) and patients <3 mos or >65 yo are at increased risk
    • Extend work up
    • Treat with abx more liberally because of higher risk of cryptosporidium, Cyclospora, cystoisospora, microsporidia, and MAC.
    • IDSA recommend abx therapy in immunocompromised patients and avoidance of probiotics due to lack of evidence.
    • Loperamide is safe in these patients with acute watery diarrhea
  • Patients on PPI and H2 blockers
    • Increasing evidence that these meds increase susceptibility to viral and bacterial pathogens.
    • Suspension of these meds in patients with AGE is reasonable.
    • No formal guidelines on this.
  • Post infectious irritable bowel syndrome results in persistent abdominal pain and diarrhea after an episode of AGE
    • Management is supportive


  • OK for discharge if vitals are better after fixing dehydration and tolerating oral hydration. Remember to treat electrolyte abnormalities.
  • Higher risk patients (<3 mos, >65 yo, immunocompromised) should be considered for admission until they demonstrate clinical improvement.

Last Updated on January 25, 2023

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