Textbook of Urgent Care Medicine, Chapter 24, Nausea, Vomiting, and Diarrhea in the Adult Patient

Published on October 26, 2026

Original author: William Gluckman

Originally published in 2014. Substantially updated and clinically reviewed in 2026 to reflect current evidence, guidelines, and urgent care practice.

Introduction

Vomiting and diarrhea may be associated with many gastrointestinal (GI) disorders, both infectious and noninfectious, but may also be symptoms associated with several other disorders and disease entities. A thorough medical history is very important in evaluating the cause for these symptoms.

In urgent care, the immediate tasks are to identify dehydration, recognize patients who may have a surgical, vascular, cardiac, metabolic, neurologic, pregnancy-related, or severe infectious process, and determine who can be treated symptomatically versus who needs emergency evaluation.

Presentation

Vomiting
Diarrhea
Abdominal pain and/or cramps
With or without fever

Triage Pearls

Look first for findings that suggest shock, a surgical abdomen, significant bleeding, severe infection, or another non-GI emergency.

Hypotension, syncope, altered mental status, severe weakness, or poor perfusion
Persistent tachycardia or inability to tolerate oral fluids
Severe or localized abdominal pain, guarding, rebound, or marked distention
Bilious or feculent emesis
Hematemesis, melena, or grossly bloody stool
Chest pain, shortness of breath, diaphoresis, or other concern for acute coronary syndrome
Severe headache, focal neurologic deficit, or meningismus
Pregnancy with significant pain, bleeding, dehydration, or persistent vomiting
Older age, immunocompromise, major comorbidity, or recent hospitalization with a toxic appearance

History Pearls

Has the patient traveled recently? This suggests the possibility of infectious diarrhea.
Has the patient come into contact with anyone who is ill? This may indicate viral gastroenteritis.
Is the diarrhea bloody or nonbloody? Bloody diarrhea raises concern for invasive bacterial infection, Shiga toxin-producing E. coli (STEC), inflammatory bowel disease, or another inflammatory process.
Ask about recent antibiotics, healthcare exposure, or prior C. difficile infection.
Ask whether the patient can keep down fluids and when they last urinated.
Obtain a surgical history. Prior abdominal or pelvic surgery increases the risk of adhesive bowel obstruction.
Ask about atrial fibrillation or vascular disease when pain is severe or out of proportion to the abdominal examination.
Ask about alcohol, cannabis, opioids, GLP-1 receptor agonists, metformin, colchicine, digoxin, chemotherapy, and other medications or supplements that can cause nausea, vomiting, or diarrhea.
Ask about food and water exposures, sick contacts, outbreaks, raw or undercooked foods, unpasteurized products, shellfish, and recent international travel.
If pregnancy is possible, establish the last menstrual period, pregnancy status if known, and the presence of pelvic pain or vaginal bleeding.

Physical Exam Pearls

How does the patient look—comfortable or toxic?
Assess vital signs, mental status, mucous membranes, skin perfusion, and urine output history for dehydration and systemic illness.
Abdominal distention may occur with obstruction or ileus.
Focal tenderness may help localize the diagnosis; guarding or rebound should raise concern for a surgical process.
Check for jaundice, pallor, or signs of GI bleeding.
Perform a focused cardiopulmonary examination when the history suggests cardiac ischemia, heart failure, pneumonia, or another extra-abdominal cause.
Orthostatic vital signs may support volume depletion but should not be used in isolation to determine severity.

Testing Pearls

Testing should be directed by the history, examination, severity, duration, and comorbidities. Most uncomplicated, short-duration gastroenteritis does not require broad laboratory testing.

Fingerstick glucose: obtain when diabetes, altered mental status, prolonged poor intake, or another metabolic cause is possible.
Pregnancy testing: obtain when pregnancy is possible and the result would change the differential diagnosis, imaging, or medication plan.
Chemistry/renal function: consider with moderate to severe dehydration, prolonged symptoms, kidney disease, diuretic use, significant comorbidity, or concern for electrolyte disturbance.
CBC: consider with significant bleeding, severe infection, suspected inflammatory disease, or concern for hemolytic uremic syndrome (HUS).
Lipase is preferred to amylase when acute pancreatitis is suspected.
ECG is appropriate when symptoms may be cardiac, significant electrolyte disturbance is suspected, or QT-prolonging antiemetics are being considered in a higher-risk patient.

Stool testing is selective, not routine.

Clinical setting	Urgent care approach
Uncomplicated acute watery diarrhea	Usually no stool testing; supportive care.
Fever, bloody/mucoid stool, severe abdominal cramping/tenderness, or sepsis	Test for invasive enteric pathogens and STEC/Shiga toxin using the locally available culture/molecular strategy.
Recent antibiotics or healthcare exposure with new unexplained >=3 unformed stools/24 h	Test one unformed stool for C. difficile using the laboratory’s recommended NAAT/toxin algorithm.
Persistent diarrhea >=14 days, immunocompromise, or relevant travel/water exposure	Consider targeted parasite/molecular testing based on exposure and duration.
Possible outbreak or public-health concern	Coordinate testing with the laboratory/public-health authority when appropriate.

Do not use fecal leukocytes or stool Gram stain to establish the cause of acute infectious diarrhea.
Do not send multiple C. difficile specimens during the same episode; routine repeat testing within 7 days and testing for cure are not recommended.

Imaging Pearls

Imaging is not routinely indicated for uncomplicated gastroenteritis.
Suspected acute small-bowel obstruction: CT abdomen/pelvis with IV contrast is generally the preferred initial study; routine oral contrast is not required and may delay care.
Suspected biliary disease: right upper quadrant ultrasound is the usual first imaging study.
Suspected acute mesenteric ischemia: CTA abdomen/pelvis with IV contrast is the preferred imaging test and requires emergency evaluation.
Plain abdominal radiographs have a more limited role than in 2014 and should not be used to delay CT or transfer when a serious intra-abdominal process is suspected.

Diagnosis Pearls

Viral gastroenteritis

Often causes acute vomiting and nonbloody diarrhea, with or without fever.
A history of similar illness in household or community contacts is common.
Most cases are self-limited; dehydration risk is higher in older adults and patients with significant comorbidity.

Inflammatory or bacterial diarrhea

Fever, blood or mucus, severe abdominal pain, or sepsis should prompt targeted stool testing rather than diagnosis by appearance alone.
Empiric antibiotics are not routine for most immunocompetent adults while results are pending.
Avoid antibiotics when STEC O157 or another Shiga toxin 2-producing STEC is suspected or confirmed because of potential harm and HUS risk.

Clostridioides difficile infection

Think of CDI with new unexplained diarrhea after antibiotics, healthcare exposure, or prior CDI; community-associated disease also occurs.
Test only symptomatic patients with clinically significant unformed stools. A positive molecular test must be interpreted in the clinical context because colonization occurs.
For a confirmed initial nonfulminant episode managed as an outpatient, fidaxomicin is preferred when feasible; oral vancomycin is an acceptable alternative. Severe systemic illness, ileus, hypotension, megacolon, marked kidney injury, or inability to hydrate warrants ED/hospital care.

Bowel obstruction

Often occurs in patients with prior abdominal surgery.
May cause crampy pain, distention, obstipation, and bilious or feculent vomiting.
Suspected obstruction is a potential surgical emergency; transfer for CT and surgical evaluation when imaging and definitive care are not immediately available onsite.

Acute mesenteric ischemia

Risk is increased with atrial fibrillation and vascular disease.
Pain may initially be severe and out of proportion to the examination; normal early examination or laboratory results do not exclude it.
Do not delay ED transfer for serial outpatient testing; CTA is the key diagnostic study in a stable patient.

GI bleeding

Hematemesis or coffee-ground emesis suggests an upper GI source.
Melena usually suggests upper GI bleeding, although brisk upper bleeding may present with hematochezia.
Hemodynamic instability, ongoing significant bleeding, syncope, severe anemia symptoms, or anticoagulation with active bleeding warrants emergency evaluation.

Nausea and vomiting of pregnancy should be distinguished from other causes, particularly when onset is late, pain or fever is present, or the presentation is atypical.
Hyperemesis gravidarum should be considered when persistent vomiting causes inability to maintain hydration, weight loss, or metabolic abnormalities.
Doxylamine-pyridoxine is the usual first-line medication strategy; other antiemetics can be used based on severity, prior response, and pregnancy-specific risk/benefit discussion.
Patients requiring IV hydration after prolonged vomiting may require thiamine before or with dextrose-containing fluids.

Treatment and Disposition Pearls

Rehydration is the foundation of treatment.

For mild to moderate dehydration, use oral rehydration solution (ORS) as first-line therapy. In mild illness, other tolerated fluids may be adequate, but very sugary drinks can worsen osmotic diarrhea.
If oral intake fails or dehydration is more significant, give isotonic crystalloid in measured boluses and reassess after each bolus. Use smaller, more cautious boluses in older adults and patients with heart failure or kidney disease.
Restart a regular diet as tolerated; prolonged bowel rest or a restrictive BRAT-type diet is not necessary.

Antiemetics

Ondansetron is commonly used to facilitate oral hydration. Consider QT-prolongation risk in patients with known long-QT syndrome, marked electrolyte abnormalities, significant bradycardia, or multiple QT-prolonging drugs.
Metoclopramide is another option but can cause akathisia, dystonia, and other extrapyramidal effects.
In pregnancy, follow pregnancy-specific treatment principles rather than relying on the obsolete FDA letter-category system; pregnancy categories A/B/C/D/X were removed from prescription labeling beginning in 2015.

Antidiarrheals and antibiotics

After adequate hydration, loperamide can be used in immunocompetent adults with acute watery diarrhea. Avoid it with bloody diarrhea, significant fever, suspected inflammatory colitis, C. difficile, ileus, or toxic megacolon risk.
Empiric antibiotics are not recommended for most acute watery diarrhea without recent international travel.
For severe travelers’ diarrhea or dysentery, azithromycin is generally preferred; therapy should reflect travel history, severity, and local resistance patterns.
Do not give empiric antibiotics for suspected STEC-associated bloody diarrhea unless another clear indication exists.

Transfer to the ED when:

Hemodynamic instability, altered mental status, severe dehydration, or failure to improve after appropriate initial treatment
Peritoneal signs, severe localized abdominal pain, marked distention, bilious/feculent vomiting, or suspected bowel obstruction/perforation
Concern for acute mesenteric ischemia, major GI bleeding, ACS, stroke/intracranial process, DKA, or another time-sensitive diagnosis
Pregnancy with significant pain/bleeding, severe dehydration, or inability to control vomiting
Severe CDI features, sepsis, or inability to maintain hydration safely as an outpatient

Medicolegal Pearls

Document the patient’s ability or inability to tolerate oral fluids before discharge.
Do not label severe abdominal pain as gastroenteritis without considering obstruction, ischemia, appendicitis, biliary disease, pancreatitis, GI bleeding, and extra-abdominal causes.
Bloody diarrhea requires consideration of STEC; indiscriminate antibiotics or antimotility therapy may be harmful.
A normal early abdominal examination does not exclude mesenteric ischemia or another evolving surgical process.
When dehydration is treated in urgent care, document reassessment of vital signs, mental status, perfusion, symptoms, and oral tolerance before disposition.

Keywords

nausea; vomiting; diarrhea; acute gastroenteritis; dehydration; Clostridioides difficile; infectious diarrhea; bowel obstruction; mesenteric ischemia; urgent care

References

Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clin Infect Dis. 2017;65(12):e45-e80.
McDonald LC, Gerding DN, Johnson S, et al. Clinical practice guidelines for Clostridium difficile infection in adults and children: 2017 update by IDSA and SHEA. Clin Infect Dis. 2018;66(7):e1-e48.
Johnson S, Lavergne V, Skinner AM, et al. Clinical practice guideline by SHEA/IDSA: 2021 focused update guidelines on management of Clostridioides difficile infection in adults. Clin Infect Dis. 2021;73(5):e1029-e1044.
Connor BA, Leung DT. Travelers’ Diarrhea. CDC Yellow Book 2026. Centers for Disease Control and Prevention. Updated March 24, 2026.
Centers for Disease Control and Prevention. Norovirus. CDC Yellow Book 2026.
Tenner S, Vege SS, Sheth SG, et al. American College of Gastroenterology guidelines: management of acute pancreatitis. Am J Gastroenterol. 2024;119(3):419-437.
American College of Radiology. ACR Appropriateness Criteria: Suspected Small-Bowel Obstruction.
American College of Radiology. ACR Appropriateness Criteria: Imaging of Mesenteric Ischemia.
American College of Radiology. ACR Appropriateness Criteria: Right Upper Quadrant Pain.
American College of Obstetricians and Gynecologists. Nausea and Vomiting of Pregnancy. Practice Bulletin No. 189. Obstet Gynecol. 2018;131:e15-e30. Reaffirmed 2024.
US Food and Drug Administration. Pregnancy and Lactation Labeling Rule (PLLR). Effective June 30, 2015.