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Am Fam Physician. 2022;106(1):72-80

This clinical content conforms to AAFP criteria for CME.

Author disclosure: No relevant financial relationships.

Acute diarrheal disease accounts for 179 million outpatient visits annually in the United States. Diarrhea can be categorized as inflammatory or noninflammatory, and both types have infectious and noninfectious causes. Infectious noninflammatory diarrhea is often viral in etiology and is the most common presentation; however, bacterial causes are also common and may be related to travel or foodborne illness. History for patients with acute diarrhea should include onset and frequency of symptoms, stool character, a focused review of systems including fever and other symptoms, and evaluation of exposures and risk factors. The physical examination should include evaluation for signs of dehydration, sepsis, or potential surgical processes. Most episodes of acute diarrhea in countries with adequate food and water sanitation are uncomplicated and self-limited, requiring only an initial evaluation and supportive treatment. Additional diagnostic evaluation and management may be warranted when diarrhea is bloody or mucoid or when risk factors are present, including immunocompromise or recent hospitalization. Unless an outbreak is suspected, molecular studies are preferred over traditional stool cultures. In all cases, management begins with replacing water, electrolytes, and nutrients. Oral rehydration is preferred; however, signs of severe dehydration or sepsis warrant intravenous rehydration. Antidiarrheal agents can be symptomatic therapy for acute watery diarrhea and can help decrease inappropriate antibiotic use. Empiric antibiotics are rarely warranted, except in sepsis and some cases of travelers’ or inflammatory diarrhea. Targeted antibiotic therapy may be appropriate following microbiologic stool assessment. Hand hygiene, personal protective equipment, and food and water safety measures are integral to preventing infectious diarrheal illnesses.

Acute diarrheal disease is a common cause of clinic visits and hospitalizations. In the United States, diarrhea accounts for an estimated 179 million outpatient visits, 500,000 hospitalizations, and more than 5,000 deaths annually, resulting in approximately one episode of acute diarrheal illness per person per year.15

RecommendationSponsoring organization
Do not order a comprehensive stool ova and parasite microscopic examination on patients presenting with diarrhea lasting less than seven days who have no immunodeficiency and no history of living in or traveling to endemic areas where gastrointestinal parasitic infections are prevalent. If symptoms of infectious diarrhea persist for seven days or more, start with molecular or antigen testing and next consider a full ova and parasite microscopic examination if other result is negative.American Society for Clinical Laboratory Science

Diarrhea is the passage of three or more loose or watery stools in 24 hours.57 Acute diarrhea is when symptoms typically last fewer than two weeks; however, some experts define acute as fewer than seven days, with seven to 14 days considered prolonged.2 Diarrhea lasting 14 to 30 days is considered persistent, and chronic diarrhea lasts longer than one month.2,5,7,8

Diarrhea can be categorized as inflammatory or noninflammatory. Inflammatory diarrhea, or dysentery, typically presents with blood or mucus and is often caused by invasive pathogens or processes. Noninflammatory or watery diarrhea is caused by increased water secretion into the intestinal lumen or decreased water reabsorption.2

Differential Diagnosis

Noninflammatory and inflammatory diarrhea may be subsequently categorized into infectious and noninfectious causes (Table 1).2,5,9,10

Noninflammatory diarrheaInflammatory diarrhea
EtiologyInfectious: often viral, but may be bacterial and, less likely, parasitic
Noninfectious: dietary, psychosocial stressors
Infectious: frequently invasive or toxin-producing bacteria
Noninfectious: Crohn disease, ulcerative colitis, radiation enteritis
History and examinationInfectious: nausea, vomiting, abdominal discomfort
Noninfectious: nausea, abdominal discomfort, frequently without vomiting
Infectious: fever, abdominal pain, tenesmus, systemic signs and symptoms
Noninfectious: abdominal pain, tenesmus, fatigue, weight loss
Laboratory findingsInfectious: often not performed; positive PCR or NAAT result
Noninfectious: negative PCR or NAAT result, positive specific laboratory testing (e.g., antitissue transglutaminase antibody)
Infectious: positive PCR or NAAT result
Noninfectious: negative PCR or NAAT result; positive for fecal calprotectin*
Common infectious pathogensBacterial: enterotoxigenic Escherichia coli, Clostridium perfrin-gens, Bacillus cereus, Staphylococcus aureus, Vibrio cholerae
Viral: Rotavirus, Norovirus
Parasitic: Giardia, Cryptosporidium
Bacterial: Salmonella, Shigella, Campylobacter, Shiga toxin–producing E. coli, entero-invasive E. coli, Clostridioides difficile, Yersinia
Parasitic: Entamoeba histolytica

Infectious noninflammatory diarrhea, the most common presentation, is typically viral in etiology, but bacterial causes are also common and are usually related to travel or foodborne illness.9,11,12

Infectious inflammatory diarrhea is more severe and is typically caused by invasive or toxin-producing bacteria, although viral and parasitic causes exist.12 Bloody stools, high fever, significant abdominal pain, or duration longer than three days suggests inflammatory infection. The most identified inflammatory pathogens in North America are Salmonella, Campylobacter, Clostridioides difficile, Shigella, and Shiga toxin–producing Escherichia coli.2,12

Specific pathogenic causes differ based on location, travel or food exposures; work or living circumstances (e.g., health care, long-term care settings); and comorbidities, such as HIV or other immunocompromised states.

Noninfectious causes of diarrhea include dietary intolerance, adverse medication effects, abdominal surgical processes such as appendicitis or mesenteric ischemia, thyroid or other endocrine abnormalities, and gastrointestinal diseases, such as Crohn disease or ulcerative colitis10,12 (Table 28,10,12). Although many of these processes are chronic, they can present acutely and should be included in the differential diagnosis of acute diarrhea.

Potential causesExamples
Abdominal processesAppendicitis, ischemic colitis, malignancy
DietaryAlcohol, caffeine, celiac disease (autoimmune), FODMAP malabsorption, lactose intolerance, nondigestible sugars
Endocrine abnormalitiesAdrenal dysfunction, bile acid malabsorption, pancreatic exocrine insufficiency, thyroid dysfunction
FunctionalIrritable bowel syndrome, mental health comorbidities, overflow diarrhea due to fecal impaction
InflammatoryCrohn disease, microscopic colitis, radiation enteritis, ulcerative colitis
Medication effectsAntibiotics, antineoplastic drugs, behavioral health medications (e.g., selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, norepinephrine-dopamine reuptake inhibitors), hypoglycemic agents, magnesium-containing products

Initial Evaluation

In countries with adequate food and water sanitation, most episodes of acute diarrhea are uncomplicated and self-limited, requiring only an initial evaluation and supportive treatment.2,6,12 The history and physical examination in patients with acute diarrhea should assess symptom severity, potential disease etiology, and personal risk factors for complications and should guide additional workup and treatment decisions.2 Figure 1 provides an approach to the evaluation and management of acute diarrhea.2,5

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