Diarrhoeal Diseases: Comprehensive Clinical Assessment, Rehydration, Diagnosis and Management

Clinical Medicine Year 3 • acute, persistent and chronic diarrhoeal syndromes

The first emergency is dehydration. Replace fluid and electrolytes immediately while investigating the cause. A stool result must never delay resuscitation in shock, severe dehydration, cholera or sepsis.

Why diarrhoea is a clinical syndrome, not one diagnosis

Diarrhoea can be caused by viruses, bacteria, protozoa, helminths, toxins, medicines, malabsorption, inflammation, endocrine disease or malignancy. The same patient may move from watery secretory diarrhoea to hypovolaemic shock, dysentery, haemolytic uraemic syndrome or severe malnutrition. Management starts with physiology—mental state, perfusion, urine and dehydration—then identifies the organism and the reason the illness persists.

Learning outcomes

Define acute, persistent and chronic diarrhoea and classify watery, inflammatory, fatty and osmotic patterns.
Explain secretory, osmotic, invasive, malabsorptive and motility mechanisms.
Assess dehydration and shock in adults, children, older people, pregnancy and severe malnutrition.
Use Plan A, Plan B and Plan C rehydration principles and calculate ongoing losses.
Recognise cholera, shigellosis, amoebiasis, enteric fever, C. difficile, giardiasis and HIV-associated diarrhoea.
Choose stool, blood, electrolyte, imaging and endoscopic investigations appropriately.
Use antibiotics, zinc, nutrition and infection-control measures selectively and safely.

1. Definition and classification

Diarrhoea is passage of three or more loose or liquid stools in 24 hours, or more frequent stools than is normal for that person. In infants, stool frequency must be judged against the child’s usual pattern; breastfed infants normally pass soft stools.

Classification	Duration/appearance	Main clinical question
Acute diarrhoea	Less than 14 days	Is there dehydration, dysentery, cholera or sepsis?
Persistent diarrhoea	14 days or more	Is there malnutrition, HIV, parasite, post-infectious injury or inflammatory disease?
Chronic diarrhoea	More than four weeks	Is there malabsorption, IBD, endocrine disease, malignancy or medication effect?
Watery	Large-volume liquid stool without visible blood	Secretory toxin, virus, osmotic cause or cholera
Dysentery	Visible blood ± mucus, fever and tenesmus	Invasive bacteria, amoebiasis, IBD or ischaemia
Fatty/malabsorptive	Bulky, greasy, foul, difficult-to-flush stool	Giardia, pancreatic, bile or small-bowel disease

2. Causes

2.1 Infectious causes

Viral: rotavirus, norovirus, adenovirus and other viruses—common in children and outbreaks.
Invasive bacteria: Shigella, Campylobacter, non-typhoidal Salmonella, diarrhoeagenic E. coli, Yersinia and occasionally Vibrio.
Secretory bacteria: toxigenic Vibrio cholerae, ETEC and other toxin-producing organisms.
Protozoa: Entamoeba histolytica, Giardia duodenalis, Cryptosporidium, Cyclospora and Cystoisospora.
Helminths and other infections: worms, HIV-associated infections, TB, CMV colitis and disseminated fungal disease.

2.2 Non-infectious causes

Antibiotics and C. difficile, metformin, laxatives, magnesium, chemotherapy, inflammatory bowel disease, coeliac disease, lactose intolerance, pancreatic insufficiency, hyperthyroidism, adrenal disease, colorectal cancer, microscopic colitis, bile-acid diarrhoea, short bowel and functional disorders.

3. Pathophysiology

3.1 Secretory diarrhoea

Enterotoxins activate chloride and bicarbonate secretion; water follows osmotically. Stool volume remains high even when the patient stops eating. Cholera produces massive secretory losses with bicarbonate and potassium depletion.

3.2 Osmotic diarrhoea

Unabsorbed solute—lactose, poorly absorbed carbohydrates, magnesium or laxatives—retains water. Symptoms improve during fasting, although fasting is unsafe in children with acute infection.

3.3 Inflammatory/invasive diarrhoea

Organisms invade mucosa or trigger cytotoxic injury, producing fever, abdominal pain, urgency, mucus, leukocytes and blood. Mucosal damage reduces absorption and can cause protein loss.

3.4 Malabsorptive diarrhoea

Damage to villi or pancreatic/bile function causes bulky fatty stools, weight loss and deficiencies. Persistent infection can cause temporary lactose intolerance after mucosal injury.

3.5 The dehydration pathway

Loss of water, sodium, chloride, bicarbonate and potassium reduces circulating volume. Tachycardia and thirst progress to poor perfusion, acute kidney injury, metabolic acidosis, hypoglycaemia, altered consciousness, shock and death.

4. History and examination

4.1 History

Onset, frequency, volume, nocturnal symptoms, blood/mucus, tenesmus, pain and vomiting.
Fever, thirst, urine amount, dizziness, fainting, confusion, seizures and weight change.
Water source, sanitation, food, travel, outbreaks, sick contacts, raw milk/meat, antibiotics and healthcare exposure.
HIV, pregnancy, malnutrition, diabetes, kidney/heart disease, immunosuppressants and previous bowel disease.
Medication, laxative, metformin, chemotherapy and dietary history; relation to fasting or particular foods.

4.2 Examination

Assess mental state, thirst, pulse, blood pressure, capillary refill, respiratory rate, temperature, oxygen saturation, mucous membranes, eyes, tears, skin pinch, peripheral temperature, abdominal tenderness/distension and bowel sounds. Record weight, urine output and stool losses. Examine for pallor, jaundice, oedema, oral thrush, perianal disease and signs of malnutrition.

5. Dehydration assessment

Category	Typical findings	Action
No dehydration	Alert, drinks normally, moist mouth, normal eyes/skin, normal perfusion	Plan A: extra fluids, nutrition, zinc for children, safety-net
Some dehydration	Restless/irritable, thirsty, sunken eyes, dry mouth, reduced tears, skin pinch slow	Plan B: ORS under observation, reassess after four hours
Severe dehydration/shock	Lethargy/unconsciousness, unable to drink, very sunken eyes, weak pulse, cold extremities, very slow skin pinch, hypotension, oliguria	Plan C: immediate IV/IO isotonic fluid, glucose/electrolytes, urgent monitoring

Older people, obese patients, malnourished children and pregnant patients may not show classic skin-pinch or eye signs. Use perfusion, mental state, urine, weight change and response to fluids.

6. Rehydration plans

Plan A: no dehydration

Give extra safe fluid after each stool, continue breastfeeding and normal feeding, provide low-osmolarity ORS, and teach the caregiver the four rules: extra fluids, zinc for eligible children, continued feeding and when to return. Return urgently for persistent diarrhoea, increasing frequency/volume, repeated vomiting, increasing thirst, inability to drink/feed, fever, blood in stool, lethargy or worsening dehydration.

Plan B: some dehydration

Give ORS over approximately four hours according to the current IMNCI/WHO weight-band table, using frequent small sips and reassessing regularly. Replace ongoing stool losses, continue breastfeeding and restart normal feeds. If vomiting occurs, pause briefly and resume slowly; persistent vomiting or deteriorating mental state requires tube/IV management.

Plan C: severe dehydration

Start IV Ringer’s lactate or normal saline immediately. A commonly taught child protocol uses 100 mL/kg divided into 30 mL/kg then 70 mL/kg, with faster administration in older children; follow the current IMNCI table precisely for age. Give ORS by mouth or nasogastric tube as soon as the child can drink, reassess perfusion every 15–30 minutes initially and hourly thereafter, and treat hypoglycaemia, electrolyte disturbance and sepsis.

If IV access is delayed: refer urgently, give ORS by mouth or nasogastric tube according to the current protocol if the airway is protected, and do not leave a severely dehydrated patient unmonitored.

Adults and cholera

Adults with profuse cholera stool may lose litres per hour. Use rapid IV crystalloid for severe dehydration, ORS for ongoing losses, urine-output monitoring and stool-volume replacement. Antibiotics are reserved for guideline-defined severe cholera/selected cases and do not replace fluids.

7. Nutrition and zinc

Continue breastfeeding frequently; breast milk is safe and protective.
Continue age-appropriate food during and after rehydration; add an extra meal daily during recovery.
Give zinc to children using the current Uganda/WHO age-based dose and duration.
Assess oedema, MUAC, weight-for-age and appetite; severe acute malnutrition requires a modified fluid and feeding pathway.
Do not routinely dilute feeds or withhold lactose unless persistent post-infectious intolerance is demonstrated.

8. Common bacterial and protozoal syndromes

8.1 Cholera

Sudden painless, profuse watery “rice-water” stool, vomiting, intense thirst, leg cramps, sunken eyes, weak pulse and rapid shock suggest cholera. Fever is often absent. Notify public health, institute infection control, obtain stool testing where feasible and start rehydration immediately. Antibiotics shorten illness in severe cases but are selected by current local guidance and susceptibility.

8.2 Shigellosis/dysentery

Fever, cramps, tenesmus and frequent small stools with blood/mucus suggest invasive colitis. Complications include dehydration, seizures in children, toxic megacolon, bacteraemia and haemolytic uraemic syndrome. Use stool culture/PCR where possible and guideline-directed antibiotics; avoid antimotility agents in inflammatory diarrhoea.

8.3 Amoebic colitis

Entamoeba histolytica causes gradual dysentery, abdominal pain and tenesmus, and can produce a liver abscess. Microscopy cannot reliably distinguish pathogenic E. histolytica from non-pathogenic species; antigen/PCR is more specific where available. Treat invasive disease with a tissue-active agent followed by a luminal eradication agent according to the guideline.

8.4 Giardiasis

Foul, greasy, bloating diarrhoea, weight loss and post-infectious lactose intolerance suggest Giardia. Ask about untreated water, daycare and household clustering; use stool antigen/PCR or repeated microscopy and treat according to local protocol.

8.5 Antibiotic-associated/C. difficile disease

Recent antibiotics, hospital exposure, watery diarrhoea, fever, leucocytosis and abdominal tenderness suggest C. difficile. Stop unnecessary antibiotics, test unformed stool only, assess severity/ileus and use current guideline treatment. Fulminant colitis, toxic megacolon, hypotension or rising creatinine needs urgent specialist/surgical review.

9. Investigations

Stool culture/PCR: dysentery, cholera/outbreak, severe or persistent disease, immunocompromise, travel, suspected enteric fever or treatment failure.
Stool microscopy/antigen: ova/parasites, Giardia, amoebiasis or Cryptosporidium where available; collect more than one sample for intermittent shedding.
Blood culture: fever/sepsis, suspected enteric fever, immunocompromise or extra-intestinal infection.
FBC, electrolytes, glucose, urea/creatinine, bicarbonate and lactate: severe dehydration, shock, persistent diarrhoea or comorbidity.
HIV test: chronic/persistent diarrhoea, weight loss, recurrent infection or other risk; investigate opportunistic organisms.
Imaging/endoscopy: peritonitis, obstruction, severe pain, abscess, inflammatory bowel disease, malignancy or chronic unexplained diarrhoea.

Do not delay ORS/IV fluid while waiting for a stool result. A negative stool test after antibiotics does not exclude infection.

10. Selective antimicrobial treatment

Most acute watery viral diarrhoea needs rehydration, nutrition and observation—not antibiotics. Use antibiotics when there is severe cholera under local policy, dysentery with systemic illness, confirmed or strongly suspected enteric fever, a susceptible extra-intestinal infection, severe immunocompromise or a defined protozoal cause. Use current Uganda susceptibility data; avoid routine antibiotics for uncomplicated traveller’s diarrhoea and avoid antimotility drugs in bloody/high-fever illness without specialist guidance.

11. Complications

Hypovolaemic shock, acute kidney injury, metabolic acidosis and electrolyte abnormalities.
Hypoglycaemia, seizures, encephalopathy and death, especially in children.
Haemolytic uraemic syndrome after Shiga-toxin disease; monitor urine, platelets, haemoglobin and renal function.
Intestinal perforation, toxic megacolon, severe colitis, peritonitis and sepsis.
Malnutrition, growth faltering, micronutrient deficiency and persistent lactose intolerance.
Extra-intestinal bacteraemia, reactive arthritis and post-infectious irritable bowel symptoms.

12. Prevention and outbreak control

Safe water, latrines, handwashing with soap, food hygiene and safe disposal of stool/vomit.
Exclusive breastfeeding for the first six months where possible, continued breastfeeding during illness and full immunisation including rotavirus.
Use chlorine/boiling and covered storage during outbreaks; avoid raw foods and unsafe ice.
Separate contaminated laundry, disinfect surfaces and use gloves for stool/vomit care.
Notify cholera/dysentery clusters, line-list cases, test strategically, identify a common water/food source and communicate danger signs.

13. Clinical reasoning examples

Example A: child with some dehydration

A child is restless, thirsty, has sunken eyes and a slow skin pinch but is conscious and drinking. Classify as some dehydration, begin supervised Plan B ORS, reassess after four hours and continue feeding/zinc. Escalate if vomiting, lethargy or perfusion worsens.

Example B: cholera shock

An adult has profuse watery stool, cold extremities, weak pulse and oliguria. Start rapid IV crystalloid and ORS as soon as able, monitor urine and electrolytes, notify public health and add antibiotics only when the current cholera protocol indicates.

Example C: persistent diarrhoea with weight loss

Investigate HIV, parasites, malabsorption, IBD, medication, pancreatic disease and malignancy rather than repeatedly prescribing antibiotics. Assess nutrition and obtain targeted stool, blood and imaging tests.

14. Examination pearls

Rehydration saves lives; antibiotics are selective.
Blood/mucus, high fever, severe pain, persistent symptoms or immune compromise changes the diagnostic plan.
Always document reassessment after Plan B or Plan C.
In severe malnutrition, standard rapid fluids can be dangerous—use the specialised protocol.
Continue feeding and breastfeeding; starvation worsens recovery.

15. References

SlideShare: Diarrhoeal Disease — definitions, causes, dehydration classification, Plan A/B/C, zinc, feeding and danger signs.
WHO/UNICEF diarrhoea, ORS, zinc and cholera guidance.
Uganda IMNCI and current Uganda Clinical Guidelines.