Gastroenterology & Family Medicine & Infectious Diseases
Acute Diarrhea | Omicron Clinic Quebec
Acute diarrhea is defined as the passage of an abnormally high volume of loose or watery stools (≥3 unformed stools per 24 hours or a fecal volume >200–250 g/day) lasting less than 14 days. It is one of the most common conditions in medicine—an estimated 1.7 billion episodes of acute diarrhea occur worldwide each year, making this condition the second leading cause of child mortality in low-income countries. In industrialized countries such as Canada, acute diarrhea is usually mild and self-limiting (spontaneous resolution within 3–7 days), but can be severe in vulnerable populations (infants, the elderly, immunocompromised individuals). Two main pathophysiological mechanisms are traditionally distinguished: secretory diarrhea (active hypersecretion of water and electrolytes by the intestinal epithelium, independent of luminal osmolarity—persists on an empty stomach—typical of bacterial enterotoxins such as cholera or ETEC) and osmotic diarrhea (presence of non-absorbable osmotically active solutes in the intestinal lumen—ceases when fasting—typical of viral infections that alter sugar absorption). The most common cause is infectious (viral or bacterial gastroenteritis—70–80% of community-acquired acute diarrhea episodes), but other mechanisms must be considered: drug-induced, toxic (food poisoning), ischemic, post-radiation, and functional (acute anxiety, irritable bowel syndrome flare-up). The term «acute gastroenteritis» is often used interchangeably with acute infectious diarrhea, but is technically more precise when it includes nausea, vomiting, and abdominal pain in addition to diarrhea. The distinction between non-inflammatory diarrhea (watery, profuse, without fever or blood—toxic or viral mechanism) and inflammatory diarrhea (small volume, mucoid-bloody, febrile, tenesmus—bacterial invasive mechanism—infectious colitis) guides the investigation and the decision regarding antibiotic therapy.
Main causes and etiological agents
| Agent / Cause | Mechanism and clinical presentation | Epidemiology, diagnosis, and specific treatment |
|---|---|---|
| Norovirus (calicivirus) Most common viral cause - adults |
Infection of the proximal small intestine → damage to mature enterocytes of the villi (without ulceration) → malabsorption + osmotic diarrhea + hypersecretion; incubation 12–48h; symptoms: nausea + projectile vomiting + watery diarrhea + abdominal cramps + myalgias + headaches; moderate or absent fever; duration: 24–72h (self-limiting); very high contagiousness (infectious dose <18 viral particles) — major cause of outbreaks in closed settings (hospitals, long-term care facilities, cruise ships, daycares, restaurants) | Fecal-oral transmission + droplets from vomiting (aerosol); clinical diagnosis in an epidemic context; fecal multiplex PCR if in doubt or in a nosocomial context; treatment: symptomatic only—oral rehydration++; strict contact isolation (resistant to alcohol-based hand rubs—washing hands with soap and water mandatory—1,000 ppm chlorine for surface decontamination) |
| Rotavirus Primary viral cause — infants and children <5 years |
Infection of mature enterocytes of the small intestine villi → destruction → malabsorption of sugars and fats → severe osmotic diarrhea; rotavirus NSP4 protein has an enterotoxic effect (chlorine hypersecretion via Ca²⁺); incubation 1–3 days; presentation: profuse watery diarrhea (5–10 stools/day) + vomiting + moderate to high fever → rapid dehydration in infants; duration: 5–7 days | Rotavirus vaccination (Rotarix—2 doses at 2 and 4 months—Rotateq—3 doses—Quebec immunization program—reduction in rotavirus-related pediatric in-hospital mortality >85% %); diagnosis: rapid antigen test (immunochromatography) on stool or PCR; treatment: oral rehydration or IV fluids if severe dehydration (children); smectite (Smecta) may reduce the duration of diarrhea |
| Campylobacter jejuni Most common bacteria — Canada |
Invasion and inflammation of the ileal and colonic mucosa → inflammatory mucoid-bloody diarrhea; incubation period: 2–5 days; clinical presentation: profuse diarrhea, initially watery then bloody, plus severe abdominal pain (pseudochirurgical) plus high fever (38.5–40 °C) plus myalgia; duration: 5–10 days; complications: sepsis (1–3%); post-infectious Guillain-Barré syndrome (GBS—an autoimmune neurological complication occurring 1–2 weeks later—30–40% of GBS cases are post-Campylobacter); reactive arthritis (Reiter’s syndrome) | Source: undercooked poultry (chicken—the primary source in Canada), untreated water, raw milk, animals (dogs, cats); stool culture + antibiotic susceptibility testing; treatment: azithromycin 500 mg/day × 3 days (first-line treatment—resistance to fluoroquinolones >20% in Canada) if severe diarrhea, high fever, or immunosuppression; ciprofloxacin 500 mg × 2/day × 5 days (if susceptibility confirmed); do not treat mild cases (spontaneous resolution, selection of resistance) |
| Salmonella non-typhoidal Frequent food poisoning |
Invasion of the ileal and colonic epithelium + inflammatory response (IL-8, TNF-α) → inflammatory diarrhea; incubation period 6–72 hours (average 24 hours); clinical presentation: watery diarrhea followed by inflammatory diarrhea + abdominal cramps + nausea/vomiting + moderate fever (38–39 °C); duration: 4–7 days (self-limiting in most cases); complications: bacteremia (5–10% — increased risk in immunocompromised patients, those with sickle cell disease, and infants); infectious endarteritis on aortic aneurysm (elderly patients) | Sources: undercooked eggs and egg products, poultry, reptiles (reptile pet salmonellosis), contaminated food (peanut butter — recurrent recalls); stool culture; treatment: do not treat uncomplicated forms (risk of prolonged carrier state and selection of resistance); antibiotic therapy if: fever >38.5 °C + signs of severity + immunosuppression + bacteremia → ciprofloxacin 500 mg × 2/day × 5–7 days or azithromycin 500 mg/day × 5–7 days |
| Clostridioides difficile Clostridioides difficile Antibiotic-associated diarrhea |
Intestinal microbiome perturbation by antibiotic therapy → proliferation of C. difficile (resistant spores) → production of toxins A (enterotoxin) and B (cytotoxin—more virulent) → pseudomembranous colitis → profuse diarrhea + abdominal pain + fever; severe forms: fulminant colitis with toxic megacolon + perforation + septic shock (mortality 30–50%); incubation: during antibiotic therapy or up to 8 weeks afterward; hypervirulent strain NAP1/BI/027 (ribotype 027) — binary toxin — hyperproducer — epidemics in Quebec 2003–2005 (high mortality) and periodic recurrences | Risk factors: recent antibiotic therapy (penicillins, fluoroquinolones, cephalosporins, clindamycin); hospitalization; age >65 years; long-term PPI use; immunosuppression; diagnosis: detection of toxins A+B by EIA or PCR (better sensitivity) on unformed diarrheal stools; colonoscopy if in doubt (pseudomembranes); 1st-line treatment: oral vancomycin 125 mg × 4/day × 10 days or fidaxomicin 200 mg × 2/day × 10 days (superior to vancomycin for recurrence prevention); ; Discontinuation of the causal antibiotic if possible; severe cases: vancomycin 500 mg × 4 times daily + IV metronidazole; multiple recurrent cases (>2): fecal microbiota transplantation (FMT) — cure rate 85–90% % |
| Escherichia coli enterohemorrhagic (EHEC — O157:H7) Bloody diarrhea – HUS in children |
Production of shigatoxins (Stx1 and Stx2) → damage to the vascular endothelium → non-febrile hemorrhagic colitis (characterized by bloody diarrhea without fever—or with a low-grade fever); incubation period: 3–8 days; clinical presentation: severe abdominal cramps + diarrhea that is initially watery and then bloody (profuse, «beef broth» appearance) + no fever or mild fever; duration: 5–10 days; major complication: hemolytic uremic syndrome (HUS)—5–10% of infected children—microangiopathic hemolytic anemia + thrombocytopenia + acute renal failure—mortality 3–5% | Sources: undercooked ground beef (hamburgers), raw milk, unpasteurized cider, contaminated leafy greens (lettuce, spinach); notifiable to public health; stool culture on selective medium + Shiga toxin PCR; fecal multiplex PCR (FilmArray GI) detects ECEH; treatment: antibiotics are contraindicated (risk of bacterial lysis → massive release of shiga toxins → increased risk of HUS); symptomatic treatment + IV rehydration + renal monitoring (creatinine, CBC, LDH) + hemodialysis if ARF |
| Foodborne illness from preformed toxin S. aureus, B. cereus, C. perfringens |
Staphylococcus aureus (heat-stable enterotoxin): very short incubation 1–6h → nausea + explosive vomiting + cramps → short diarrhea (6–12h); source: poorly refrigerated protein-rich foods (cold cuts, mayonnaise, pastry cream); ; Bacillus cereus (emetic syndrome: thermostable cereulide toxin — 1–6h; diarrheal syndrome: enterotoxin — 8–16h); source: reheated rice, pasta, cereals; ; C. perfringens (enterotoxin released during sporulation in the intestine): incubation 8–16h → cramps + profuse watery diarrhea + rare vomiting → resolution 24h; source: pre-cooked meats and poultry | Clinical picture is highly suggestive (short incubation, context of communal meal, rapid recovery); coproculture not useful (preformed toxin - not strictly infectious); report to INSPQ if group cases (collective food poisoning - TIAC); treatment: symptomatic only - oral rehydration; antiemetics (ondansetron, domperidone) if intense vomiting |
| Non-infectious causes | Medications (antibiotics — ampicillin, amoxicillin-clavulanate, macrolides → diarrhea due to microbiome disruption or prokinetic effect — erythromycin motilin agonist; PPIs; metformin; colchicine; magnesium; laxatives); mesenteric ischemia (elderly patient with chronic mesenteric ischemia — sudden bloody diarrhea); post-radiation (after pelvic radiotherapy — acute actinic colitis); functional diarrhea or IBS flare-up (acute anxiety, stress, colitis); decompensated lactose intolerance (osmotic diarrhea); Crohn's disease or ulcerative colitis flare-up | Medical history and digestive history are essential; consider ischemic colitis in the elderly patient with sudden bloody diarrhea + left flank abdominal pain (splenic flexure - watershed area) without high fever; abdominal CT scan if ischemia is suspected. |
Dehydration Assessment and Rehydration
- Mild dehydration (<5% of body weight): mild dryness of the mucous membranes, increased thirst, mild oliguria — treatment: ORS (oral rehydration solution) ad libitum at home — 200–400 mL after each episode of watery diarrhea in adults; children: 50–100 mL/kg over 4 hours for those weighing <10 kg, 50 mL/kg for those weighing >10 kg
- Moderate dehydration (5–10% body weight loss): dry mucous membranes, persistent skin turgor, dark circles under the eyes, sunken fontanelle (in infants), marked oliguria, tachycardia — treatment: 50–100 mL/kg of oral rehydration solution (ORS) over 3–4 hours (intensive oral rehydration technique) in the clinic or emergency department; IV infusion if uncontrollable vomiting or failure of ORS
- Severe dehydration (>10% body weight loss): very slow skin turgor, cold extremities, hypotension, severe tachycardia, altered consciousness, anuria — Medical emergency — IV infusion of 0.9% NaCl, 1% TPA, 3% TPA, administered as a rapid bolus of 20 mL/kg + monitoring
- WHO Oral Rehydration Solution (ORS): Na⁺ 75 mmol/L + K⁺ 20 mmol/L + citrate 10 mmol/L + glucose 75 mmol/L + osmolarity 245 mOsm/L (low osmolarity ORS - higher than older formula to reduce vomiting); available in pharmacies (Pedialyte, Gastrolyte); avoid fruit juices and sugary drinks (high osmolarity - worsens osmotic diarrhea)
- Diet: resume normal eating quickly (as soon as digestive tolerance allows — historical BRAT diet — banana, rice, applesauce, toast — not recommended by current pediatric societies due to being low in calories); avoid foods high in insoluble fiber, fats, and dairy for 24–48 hours in severe cases.
Symptomatic treatment and antibiotics
| Treatment | Mechanism and dosage | Indications and contraindications |
|---|---|---|
| Loperamide (Imodium) Symptomatic antidiarrheal |
Agonist of intestinal µ-opioid receptors → reduction in peristalsis + reduction in intestinal secretion + increased anal sphincter tone; adult dosage: 4 mg initially then 2 mg after each loose stool — maximum 16 mg/day; onset of action: 1–3h; efficacy: significant reduction in stool frequency and diarrhea duration (Cochrane 2019) | Indicated in non-inflammatory acute diarrhea (watery, without fever or blood) in adults; ; contraindicated in: inflammatory / bloody / febrile diarrhea (risk of toxic megacolon — paralytic ileus with toxin accumulation); C. difficile colitis; children Under 2 years (risk of respiratory distress and intestinal paralysis); pregnancy (1st trimester); restricted to adults with functional diarrhea during travel (non-inflammatory traveler's diarrhea) |
| Racecadotril (Tiorfan) Antisecretory - Pediatrics |
Intestinal enkephalinase inhibitor → increased endogenous enkephalins → reduced intestinal secretion (cAMP and cGMP) without reducing peristalsis (unlike loperamide — lower risk of megacolon); pediatric dosage: 1.5 mg/kg x 3/day (10 mg sachets) — approved for children >3 months; adult: 100 mg x 3/day | Preferred over loperamide in children due to a more favorable safety profile; in combination with ORS (Cochrane trial 2019 - reduction in diarrhea duration and stool volume); not contraindicated in mild febrile cases (does not block peristalsis); available in pharmacies in Canada |
| Probiotics Lactobacillus rhamnosus GG — Saccharomyces boulardii |
Competitive microbiome restoration — multiple mechanisms (lactic acid and bacteriocin production — inhibition of enteropathogens; stimulation of secretory IgA; reduction of intestinal permeability); reduction in the duration of acute infectious diarrhea by approximately 1 day (Cochrane meta-analysis Allen 2010 — 63 trials — LGG and S. boulardii best documented); ; Saccharomyces boulardii particularly effective in preventing antibiotic-associated diarrhea (−57 % risk reduction — Szajewska 2015 meta-analysis) | Recommended as a supplement to ORS in viral gastroenteritis in children (ESPGHAN 2014); prevention of antibiotic-associated diarrhea (S. boulardii + LGG prescribed concurrently with any antibiotic); prevention of recurrent C. difficile colitis (S. boulardii); generally well-tolerated — avoid in severely immunocompromised individuals (rare risk of S. boulardii fungemia). |
| Azithromycin Empiric antibiotic therapy — inflammatory diarrhea |
Macrolide — inhibition of bacterial translation (23S rRNA — 50S subunit); coverage: Campylobacter (1st line), Shigella, Salmonella (severe cases); dosage: 500 mg/day for 3 days (adults) or 1 g as a single dose (moderate to severe traveler’s diarrhea); Campylobacter resistance to fluoroquinolones >20% in Canada → azithromycin preferred for empirical treatment | Indicated if: febrile diarrhea + blood in stool + altered general condition ± vulnerable patient (elderly, immunocompromised, asplenia) + stay in endemic area; ; do not prescribe if EHEC O157:H7 suspected (increased risk of HUS); severe traveler's diarrhea (azithromycin 1 g single dose—equally effective and less risk of resistance selection than ciprofloxacin) |
| Ciprofloxacin Alternative — invasive bacterial diarrhea |
Fluoroquinolone — inhibition of DNA gyrase and topoisomerase IV; broad coverage (Enterobacteriaceae, Salmonella, Shigellabut increasing resistance of Campylobacter in Canada (>20,000–30,000) and in Asia (>50,000–80,000); dosage: 500 mg twice daily for 5–7 days; main use: Shigella (if sensitive), Salmonella invasive, traveler's diarrhea in low-resistance areas | Reserved for situations documented by antibiogram or in low-resistance areas; do not use empirically in Canada for community-acquired diarrhea due to increasing Campylobacter resistance; ; contraindicated E. coli O157:H7 (HUS risk); QT prolongation if combined with other QT-prolonging drugs |
ℹ️
Visit traveler's diarrhea affects 20–60% of travelers to countries with poor sanitation (Africa, South Asia, Latin America, the Middle East) — the majority of cases (80–90%) are bacterial (ETEC being the most common, followed by Campylobacter, Salmonella, ShigellaPrevention relies on dietary precautions (bottled or boiled water, hot cooked food, avoiding raw vegetables and unpeeled fruits - the «cook it, boil it, peel it, or forget it» rule) and not on prophylactic antibiotics (reserved for immunocompromised individuals). Treatment for moderate to severe traveler's diarrhea: azithromycin 1 g by mouth in a single dose (ISTM 2017 - International Society of Travel Medicine recommendation) ± loperamide if non-bloody, non-febrile diarrhea. Rifaximin (Xifaxan - 200 mg x 3/day x 3 days) is an effective non-absorbable alternative (ETEC) but without activity on Campylobacter invasive.
Warning Signs — Urgent Consultation or 911
Consult immediately to the emergency room you compose the 911 if diarrhea is accompanied by any of these signs: severe dehydration (hypotension, confusion, cold extremities, anuria); abundant bright red blood in stools (massive rectal bleeding); fever >39.5°C persisting despite antipyretics; intense abdominal pain, abdominal rigidity (defense) or wooden abdomen (perforation or peritonitis); altered consciousness or convulsions (especially in infants - hypernatremic dehydration); profuse diarrhea in an infant Less than 3 months.
Consult your doctor within 24 hours if: bloody or mucopurulent diarrhea + fever (>38.5 °C) in an adult; diarrhea lasting >7 days with no improvement; weight loss >5% of body weight; recent return from travel to a tropical area; recent antibiotic therapy (suspect C. difficile) ; immunosuppression (HIV, transplant, chemotherapy).
Consult at Clinique Omicron
Clinique Omicron physicians evaluate and manage acute diarrhea—clinical examination, assessment of dehydration severity, prescription of stool cultures and fecal multiplex PCR tests if indicated, targeted antibiotic therapy based on identified agents, and prevention advice (traveler's diarrhea, rotavirus vaccination, food hygiene). Consultations are available at our service points in Quebec as well as through telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not substitute for professional medical advice from a qualified healthcare provider. Any diarrhea accompanied by blood, high fever, or signs of dehydration requires prompt medical evaluation.
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