Acute Diarrhoea and Gastroenteritis

Name: Acute Diarrhoea and Gastroenteritis
Creator: MedVellum Editorial Team

1. Clinical Overview

Summary

Acute diarrhoea is defined as the passage of three or more loose or watery stools per day (or more frequent than normal for the individual) lasting less than 14 days. [1] It is a leading cause of outpatient visits and work absenteeism, with most cases in adults being viral and self-limiting. [2]

The primary clinical challenge is identifying high-risk cases that require investigation (e.g., C. difficile, STEC, or invasive bacteria) while practicing antibiotic stewardship. Management focuses on oral rehydration therapy (ORT) and the selective use of anti-motility agents. [3] Guidelines from NICE (NG199) and the BSG emphasize the shift towards Vancomycin or Fidaxomicin as first-line for C. difficile, replacing the historical use of Metronidazole. [4,5]

Key Facts

Norovirus Predominance: Norovirus is the leading cause of infectious gastroenteritis in adults, often causing explosive vomiting and watery diarrhoea. [2]
The "SGLT1" Basis: Oral rehydration works because the glucose-sodium co-transporter (SGLT1) remains functional even during viral/bacterial insult, allowing water to follow salt absorption. [6]
Antibiotic Paradox: Routine antibiotics are NOT indicated for most bacterial cases (e.g., Salmonella) as they can prolong faecal shedding and increase the risk of a carrier state. [7]
STEC/HUS Warning: Antibiotics should be avoided in suspected E. coli O157:H7 (STEC) infection, as they may trigger a massive release of Shiga toxin, precipitating Haemolytic Uraemic Syndrome (HUS). [8]
48-Hour Rule: Public health guidelines require food handlers and healthcare workers to be excluded from work until 48 hours symptom-free. [9]

Clinical Pearls

The "Vomiting-First" Pearl: If vomiting is the dominant initial symptom followed by watery diarrhoea in a household cluster, think Norovirus. If vomiting occurs within 6 hours of a specific meal, think pre-formed toxins (S. aureus or B. cereus). [10]

The "C. diff Smell" Pearl: While often described as "horse-stable" or "sickly sweet," do not rely on smell for diagnosis. Any patient with diarrhoea and recent antibiotic use (up to 3 months prior) requires a C. difficile toxin test. [4]

The "Loperamide" Warning: Never give Loperamide to patients with bloody diarrhoea, high fever, or suspected C. difficile. Slowing transit in these cases can lead to Toxic Megacolon or increased toxin absorption. [3,11]

2. Epidemiology & Risk Factors

Incidence & Distribution

Global Burden: Approximately 1.7 billion cases of childhood diarrhoeal disease occur globally each year, but it remains a top-5 cause of GP visits in adults in developed nations. [1]
Seasonality: Norovirus peaks in winter ("Winter Vomiting Bug"); Campylobacter (the most common UK bacterial cause) peaks in late spring/summer. [12]

Risk Factors

Category	Factor	Impact
Iatrogenic	Recent Antibiotics	Disruption of microbiome allowing C. difficile overgrowth.
Iatrogenic	PPIs	Reduced gastric acid allows lower infectious doses of pathogens to survive.
Exposure	Foreign Travel	High risk of ETEC, Giardia, or Salmonella typhi.
Exposure	Undercooked Poultry	Primary risk for Campylobacter.
Host	Age > 65	Higher risk of severe dehydration and AKI.

3. Pathophysiology

1. Secretory vs. Osmotic

Secretory: Pathogens (e.g., Vibrio cholerae, ETEC) produce toxins that stimulate cAMP/cGMP, opening chloride channels (CFTR). Water follows chloride into the lumen. Diarrhoea persists even during fasting. [13]
Osmotic: Viral damage to villi tips causes malabsorption of carbohydrates (e.g., lactose). Unabsorbed solutes pull water into the lumen. Diarrhoea improves with fasting.

2. Inflammatory (Dysentery)

Invasive pathogens (Shigella, Campylobacter, Salmonella) invade the mucosa, causing cell death, recruitment of neutrophils, and bleeding. This results in the classic small-volume, bloody, mucoid stools of dysentery. [14]

3. Post-Infectious IBS

Approximately 10% of patients develop Post-Infectious Irritable Bowel Syndrome (PI-IBS) following a bacterial flare, likely due to low-grade mucosal inflammation and altered gut-brain signaling. [15]

4. Clinical Presentation

Symptoms

Watery Diarrhoea: Suggests viral or toxigenic bacterial cause.
Bloody Diarrhoea: Suggests invasive bacteria (Campylobacter, Shigella, STEC) or IBD.
Tenesmus: Suggests rectal inflammation (typical of Shigella or UC).
Vomiting: Prominent in Norovirus and food poisoning.

Physical Signs

Hydration Status: Check mucous membranes, skin turgor, and capillary refill.
Tachycardia/Hypotension: Markers of severe volume depletion.
Abdominal Tenderness: Usually diffuse; localized guarding suggests perforation or toxic megacolon.

5. Investigations

1. Bedside

Vital Signs: Mandatory.
Urine Dipstick: High specific gravity indicates dehydration.

2. Laboratory (If indicated)

U&Es: To check for AKI and hypokalaemia.
CRP: Often > 100 mg/L in invasive bacterial infections.
FBC: Look for anaemia or thrombocytopenia (low platelets + AKI = HUS).

3. Stool Studies (The "Trigger" List)

Do NOT send stool for everyone. Send if:

Red Flags: Blood in stool, high fever, or systemic upset.
History: Recent travel, recent antibiotics, or hospital admission.
Persistence: Symptoms > 7 days.
Occupation: Food handlers or healthcare workers. [3,9]

6. Management: The Acute Diarrhoea Algorithm

Management Flowchart (ASCII)

                  [ACUTE DIARRHOEA (less than 14 DAYS)]
                             |
              +--------------v--------------+
              |    CLINICAL ASSESSMENT      |
              | (Vitals, Hydration, History)|
              +--------------+--------------+
                             |
              /--------------+--------------\
      [SEVERE DEHYDRATION]            [MILD/MODERATE]
      (Shock, Oliguria,               (Tolerating Orals)
       Confusion)                            |
             |                        /------+------\
      +------v------+         [RED FLAGS?]      [NO RED FLAGS]
      | IV FLUIDS   |         (Blood, Fever,           |
      | ADMISSION   |          Antibiotics)    +-------v-------+
      +-------------+                |         | SUPPORTIVE    |
                             +-------v-------+ | 1. ORS (Home) |
                             | SEND STOOL    | | 2. 48h Work   |
                             | MC&S + TOXIN  | |    Exclusion  |
                             +-------+-------+ +---------------+
                                     |
                             /-------+-------\
                    [POSITIVE C. DIFF]    [CAMPYLOBACTER]
                            |                (Severe/Persist)
                    +-------v-------+       +-------v-------+
                    | VANCOMYCIN PO |       | AZITHROMYCIN  |
                    | (125mg QDS)   |       | (500mg 3 days)|
                    +---------------+       +---------------+

1. Rehydration (First-line)

ORS: 200–400 mL after every loose stool.
IV Fluids: Only if the patient is in shock or unable to tolerate oral intake.

2. Antibiotic Strategy (Selective)

Campylobacter: Only if severe or immunocompromised (Azithromycin 500mg OD for 3 days). [16]
C. difficile: Vancomycin 125mg PO QDS for 10 days (First-line NICE NG199). [4]
Travellers' Diarrhoea: Consider Azithromycin or Rifaximin.
Salmonella: Avoid antibiotics unless septicaemic (risk of carrier state).

3. Anti-motility

Loperamide: 4mg initially, then 2mg after each loose stool (Max 16mg/day).
Contraindications: Bloody diarrhoea, high fever, C. diff. [11]

7. Complications

AKI (Prerenal): Due to severe volume depletion.
HUS: Seen in STEC; presents with the triad of Microangiopathic Haemolytic Anaemia, Thrombocytopenia, and AKI.
Guillain-Barré Syndrome: A post-infectious complication of Campylobacter (molecular mimicry). [17]
Reactive Arthritis: HLA-B27 associated; follows Salmonella or Shigella.

8. Evidence & Landmark Trials

NICE NG199 (2021): Updated guideline confirming Vancomycin/Fidaxomicin as superior to Metronidazole for C. difficile.
The PLACIDE Trial (PMID: 23927524): Large RCT showing that multi-strain probiotics provide no benefit in preventing antibiotic-associated diarrhoea or C. difficile in the elderly.
Wong et al. (PMID: 10871346): Seminal paper demonstrating that antibiotic treatment of E. coli O157 increases the risk of HUS.
The GRACE Trial (PMID: 23265993): Contextual evidence for antibiotic stewardship in primary care infections.

9. Single Best Answer (SBA) Questions

Question 1

A 74-year-old female presents with profuse watery diarrhoea and abdominal cramping. She was treated for a urinary tract infection with Clindamycin two weeks ago. What is the most appropriate first-line treatment if C. difficile is confirmed?

A) Oral Metronidazole 400mg TDS
B) Oral Vancomycin 125mg QDS
C) Intravenous Vancomycin 500mg QDS
D) Oral Fidaxomicin 200mg BD
E) Intravenous Metronidazole 500mg TDS
Answer: B. NICE NG199 (2021) recommends oral Vancomycin as the first-line treatment for a first episode of C. difficile.

Question 2

A 22-year-old male returns from a backpacking trip to Southeast Asia with bloody diarrhoea, tenesmus, and high fever (39.1°C). Stool culture shows Shigella flexneri. What is the most appropriate antibiotic?

A) Amoxicillin
B) Metronidazole
C) Azithromycin
D) Vancomycin
E) Doxycycline
Answer: C. Azithromycin is the preferred first-line agent for shigellosis due to increasing fluoroquinolone resistance.

Question 3

A 6-year-old child presents with bloody diarrhoea. The mother mentions the child ate a burger at a local fair 3 days ago. The child is now pale and has a reduced urine output. Labs show: Hb 8.2 g/dL, Platelets 45 x 10^9/L, Creatinine 180 μmol/L. What is the most likely diagnosis?

A) Acute Appendicitis
B) Henoch-Schönlein Purpura
C) Haemolytic Uraemic Syndrome (HUS)
D) Intussusception
E) Ulcerative Colitis
Answer: C. The triad of microangiopathic anaemia, thrombocytopenia, and AKI following bloody diarrhoea is diagnostic of HUS (likely STEC-related).

Question 4

In the context of acute gastroenteritis, what is the physiological basis for using Oral Rehydration Solutions (ORS) containing both glucose and sodium?

A) Glucose kills the bacteria in the gut
B) Sodium prevents the bacteria from adhering to the wall
C) Glucose activates the SGLT1 co-transporter to pull sodium and water into enterocytes
D) It prevents metabolic alkalosis
E) It reduces the duration of the cough reflex
Answer: C. The SGLT1 transporter remains functional, allowing for efficient rehydration even during diarrhoeal illness.

Question 5

A 30-year-old chef is diagnosed with Salmonella gastroenteritis. He is otherwise well and systemically stable. What is the most appropriate management?

A) Prescribe Ciprofloxacin to ensure he can return to work faster
B) Supportive care and 48-hour work exclusion after symptoms resolve
C) Immediate hospital admission for IV fluids
D) Start Metronidazole
E) Prescribe Loperamide to stop the diarrhoea immediately
Answer: B. Antibiotics are not indicated for uncomplicated Salmonella and can prolong carriage. Work exclusion is mandatory for food handlers.

Question 6

Which of the following pathogens is the most common cause of bacterial food poisoning in the UK, typically associated with undercooked poultry?

A) Staphylococcus aureus
B) Bacillus cereus
C) Campylobacter jejuni
D) Vibrio cholerae
E) Clostridioides difficile
Answer: C. Campylobacter is the most common bacterial cause in the UK.

Question 7

A 45-year-old patient presents with symptoms suggestive of Norovirus. Alcohol-based hand gel is being used by the family for hand hygiene. What advice should be given regarding Norovirus prevention?

A) Alcohol gel is the most effective way to kill Norovirus
B) Norovirus is only spread through the air, so hand hygiene is not needed
C) Soap and water is superior to alcohol gel as Norovirus is a non-enveloped virus
D) Everyone should take prophylactic antibiotics
E) The patient should stay in a room with the windows closed
Answer: C. Alcohol gel is relatively ineffective against non-enveloped viruses like Norovirus; vigorous handwashing with soap and water is required.

Question 8

A patient with a history of C. difficile infection treated with Vancomycin presents with a recurrence 2 weeks later. According to NICE NG199, what is the preferred treatment for a first recurrence?

A) A second course of Vancomycin
B) Oral Metronidazole
C) Oral Fidaxomicin
D) Faecal Microbiota Transplant (FMT)
E) Intravenous Heparin
Answer: C. Fidaxomicin is the preferred agent for recurrent C. difficile due to lower subsequent recurrence rates.

Question 9

A 28-year-old female presents with persistent abdominal bloating and altered bowel habit 3 months after a severe episode of Campylobacter gastroenteritis. Investigations for IBD and Coeliac disease are negative. What is the most likely diagnosis?

A) Chronic Campylobacter infection
B) Post-infectious Irritable Bowel Syndrome (PI-IBS)
C) Chronic Pancreatitis
D) Diverticulitis
E) Small Intestinal Bacterial Overgrowth (SIBO)
Answer: B. PI-IBS is a common sequela of bacterial gastroenteritis.

Question 10

Which electrolyte abnormality is most commonly associated with profuse watery diarrhoea and is a component of ORS replacement?

A) Hyperkalaemia
B) Hypokalaemia
C) Hypernatraemia
D) Hypocalcaemia
E) Hypermagnesaemia
Answer: B. Significant potassium is lost in diarrhoeal stools; hypokalaemia is a common complication.

10. Patient Explanation

"Acute diarrhoea is usually caused by a 'stomach bug' (a virus or bacteria) that irritates the lining of your bowel. This stops the bowel from absorbing water properly, leading to loose or watery stools. The good news is that for most healthy adults, your body is excellent at clearing these infections on its own within a few days.

The most important part of treatment is staying hydrated. We recommend using oral rehydration sachets (like Dioralyte), which contain the perfect balance of salt and sugar to help your body absorb water. You should avoid 'stopping' the diarrhoea with medicines like Loperamide if you have a fever or see blood, as your body uses the diarrhoea to flush the germs out.

To prevent spreading it to others, wash your hands thoroughly with soap and water (as gels don't always kill these bugs) and stay home from work or school until you have been completely symptom-free for 48 hours. If you notice blood, severe tummy pain, or if you can't keep any fluids down, please contact us immediately."

11. References

World Health Organization. Diarrhoeal disease. WHO Fact Sheets. 2017.
Koo HL, et al. Noroviruses: The Principal Cause of Foodborne Disease Worldwide. Discov Med. 2010. [PMID: 20670600]
Riddle MS, et al. ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults. Am J Gastroenterol. 2016. [PMID: 27068718]
NICE. Clostridioides difficile infection: antimicrobial prescribing. NG199. 2021.
Lamb CA, et al. British Society of Gastroenterology consensus guidelines on the management of inflammatory bowel disease in adults. Gut. 2019. [PMID: 31562236]
Binder HJ, et al. Oral rehydration therapy in the second decade of the twenty-first century. Curr Gastroenterol Rep. 2014. [PMID: 24436001]
Sirinavin S, et al. Antibiotic treatment for Salmonella gastroenteritis. Cochrane Database Syst Rev. 2000. [PMID: 10796333]
Wong CS, et al. The risk of the hemolytic-uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N Engl J Med. 2000. [PMID: 10871346]
Public Health England. Guidance on Infection Control in Schools and other Childcare Settings. 2017.
Argudín MA, et al. Food poisoning and Staphylococcus aureus enterotoxins. Toxins (Basel). 2010. [PMID: 22069631]
Li ST, et al. Loperamide therapy for acute diarrhea in children: systematic review and meta-analysis. PLoS Med. 2007. [PMID: 17388664]
Tam CC, et al. Longitudinal study of infectious intestinal disease in the UK (IID2 study): incidence in the community and presenting to general practice. BMJ Open. 2012. [PMID: 22315302]
Thiagarajah JR, et al. Pathogenesis of infectious diarrhea. Nat Rev Gastroenterol Hepatol. 2012. [PMID: 22805954]
DuPont HL. Acute infectious diarrhea in immunocompetent adults. N Engl J Med. 2014. [PMID: 24738670]
Thabane M, et al. Post-infectious irritable bowel syndrome. World J Gastroenterol. 2009. [PMID: 19610134]
Ternhag A, et al. A meta-analysis on the effects of antibiotic treatment on Campylobacter jejuni infection. Clin Infect Dis. 2007. [PMID: 17216601]
Yuki N, Hartung HP. Guillain-Barré syndrome. N Engl J Med. 2012. [PMID: 22694335]

Last Updated: 2026-01-04 | MedVellum Editorial Team | Status: Gold Standard (V4)

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