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IM16.1-17 | Diarrheal Disorders — PBL Case

CLINICAL SETTING

Dr Kavitha is the medical officer at a 30-bed rural community health centre (CHC) in coastal Tamil Nadu. It is 9 AM on a Tuesday in September. Over the past 18 hours, four patients from the same fishing village have been brought in with profuse watery diarrhoea. The most recent arrival is Murugan, a 45-year-old fisherman. His wife and two neighbours arrived earlier. Murugan's wife reports: 'He started vomiting and having loose stools last night after dinner. By 2 AM he could not stand up.' Murugan is now lying on the examination couch. He is conscious but very weak. His wife says the family draws drinking water from a shared open well in the village; the well had overflow from a nearby drain after heavy rain three days ago. She adds: 'One more family in our lane also has similar complaints today morning.' Final-year MBBS student Arjun is posted at the CHC for his community medicine rotation and is assisting Dr Kavitha.

Trigger 1: Examination and First Assessment

Dr Kavitha examines Murugan. He is conscious but lethargic. Vitals: BP 80/50 mmHg, pulse 118/min and thready, RR 28/min. Eyes are deeply sunken, no tears, tongue and lips are dry. Skin pinch over the abdomen retracts very slowly, taking more than 3 seconds. Temperature 36.8°C (afebrile). Abdomen is soft, non-tender, with hyperactive bowel sounds. Murugan has had 10-12 episodes of stool since midnight — described by his wife as 'like rice-water, no colour, no smell of normal stool, no blood.' He has vomited 4 times. He has not passed urine since 10 PM the previous night. Blood glucose by glucometer: 88 mg/dL. Arjun documents the findings in the case sheet and turns to Dr Kavitha: 'What is my dehydration assessment, and what do we do RIGHT NOW?'

DISCUSSION POINTS

  • Apply the WHO dehydration assessment criteria to Murugan: which grade does he meet, and what is the corresponding WHO management plan?
  • The stool is described as 'rice-water' — colourless, odourless, with no blood. Which pathophysiological mechanism does this represent, and what is the prototype causative organism that produces this appearance?
  • What is the significance of Murugan being afebrile with profuse watery diarrhoea? How does fever (or absence of fever) guide the initial diagnosis of a diarrhoeal illness?
Click to reveal Trigger 2: Rapid Diagnosis and the Laboratory (discuss previous trigger first!)

Trigger 2: Rapid Diagnosis and the Laboratory

Dr Kavitha asks Arjun to prepare a hanging-drop preparation from a fresh stool sample. Under the dark-field microscope, Arjun sees comma-shaped organisms darting rapidly across the field. Dr Kavitha adds a drop of O1 antiserum to the preparation — the motility stops completely within seconds. She confirms: 'Positive agglutination — this is cholera, O1 serotype.' Meanwhile, the nursing staff report that two of the four patients are now hypotensive. Dr Kavitha faces a difficult situation: the CHC has one functioning IV line set, limited IV fluids (4 bags of Ringer's Lactate remaining), and the nearest secondary hospital is 40 km away. She says to Arjun: 'We have a public health emergency, a resource constraint, and four severely dehydrated patients. Walk me through your priorities.' She also asks: 'Should I start antibiotics for all four patients? Which one, and why?'

DISCUSSION POINTS

  • Describe the hanging-drop preparation technique and interpret the finding: what does rapid darting motility with comma-shaped bacilli, inhibited by O1 antiserum, indicate?
  • With four severely dehydrated cholera patients and limited IV fluids, how would you triage and prioritise WHO Plan C administration? Who gets IV fluids first and at what rate?
  • What is the role of antibiotics in cholera, which antibiotic should be used, and what is the correct dosing for an adult? Is antibiotic therapy the primary treatment or secondary to rehydration?
Click to reveal Trigger 3: A Different Patient in the Same Outbreak (discuss previous trigger first!)

Trigger 3: A Different Patient in the Same Outbreak

While managing Murugan, Dr Kavitha is called to see another patient from the same village: Selvi, a 28-year-old woman, 20 weeks pregnant. Selvi has 6-8 stools per day, but unlike Murugan's clear watery stools, Selvi's stools contain mucus and she reports lower abdominal cramps and tenesmus. Her temperature is 38.6°C. There is no blood in the stool. Selvi is only mildly dehydrated (Plan A criteria). The outbreak team in the village has collected water samples from the shared well. Dr Kavitha turns to Arjun: 'Selvi's presentation is different from the others. The stool pattern is not cholera — what is going on? And does the antibiotic choice change for a pregnant woman?'

DISCUSSION POINTS

  • Selvi has mucoid stools with tenesmus and fever — not rice-water stools. What does this clinical pattern suggest, and how does it differ from cholera in terms of pathophysiology and likely pathogen?
  • How would you manage Selvi's diarrhoea given that she is 20 weeks pregnant? Which antibiotics are safe, and which should be avoided (e.g., fluoroquinolones, tetracyclines)?
  • An outbreak involves both cholera-like secretory diarrhoea (Murugan) and dysentery-like illness (Selvi) from the same water source. Is it possible for a single outbreak event to involve more than one pathogen? What does this mean for public health investigation?
Click to reveal Trigger 4: Three Weeks Later — Chronic Consequences (discuss previous trigger first!)

Trigger 4: Three Weeks Later — Chronic Consequences

Three weeks after the outbreak, Dr Kavitha's follow-up clinic has two patients returning. Murugan has recovered fully. However, a 12-year-old girl, Priya, who also had watery diarrhoea during the outbreak, continues to have loose stools 3-4 times per day with bloating, flatulence, and frothy stools. She has lost 3 kg. Her mother reports Priya's diarrhoea is worse after drinking milk. Stool microscopy shows fat globules. A second patient, Rajan, a 50-year-old man, had persistent diarrhoea for 4 weeks, and now has continued diarrhoea at 5-6 times per day, abdominal pain, and on examination has a positive faecal occult blood test. He is afebrile and not dehydrated. He lives in Chennai and had no contact with the outbreak well. Dr Kavitha refers him for colonoscopy. The report reads: 'Continuous mucosal inflammation from the rectum to the descending colon with pseudopolyps; rectum involved; biopsy: crypt abscesses, no granulomas.'

DISCUSSION POINTS

  • Priya has post-infectious diarrhoea with fat globules in stool, bloating worse after milk, and weight loss. What is the most likely mechanism, what parasite would you look for, and how would you treat her?
  • Rajan's colonoscopy shows continuous colitis from the rectum with crypt abscesses and no granulomas. What is the diagnosis, and how do these endoscopic and histological features distinguish it from Crohn's disease?
  • For Rajan's newly diagnosed condition, outline the step-up treatment ladder from first-line to biological therapy, including the mandatory pre-treatment screening before starting anti-TNF agents in an Indian patient.

Group Task Assignments

  • Design a rapid outbreak investigation protocol for a suspected cholera outbreak in a fishing village: what samples are collected, from whom, using which techniques, and what public health notifications must be made within 24 hours under the Integrated Disease Surveillance Programme (IDSP)?
  • Construct a resource-limited triage protocol for a CHC receiving multiple severely dehydrated cholera patients simultaneously with limited IV fluids: define the criteria for IV vs nasogastric vs oral rehydration, and calculate the exact fluid volume required for a 60 kg adult under WHO Plan C.
  • Compare and contrast the clinical, endoscopic, and histological features of Ulcerative Colitis versus Crohn's disease in a structured table. Include distribution pattern, depth of inflammation, histological finding, extra-intestinal manifestations, cancer risk, and curability by surgery.
  • Draft a community health education poster for a fishing village explaining how to prepare and use WHO ORS correctly, identify when to come to a health centre (red flags), and prevent the spread of cholera through water source protection.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [IM16.2] What are the WHO criteria for grading dehydration severity in adults with acute diarrhoea, and how does each grade map to a specific rehydration plan (A, B, or C) with volumes, rates, and routes?
  2. [IM16.10] Describe the technique for preparing a hanging-drop preparation for Vibrio cholerae, what is observed under dark-field microscopy, and how does antiserum agglutination confirm serotype?
  3. [IM16.14] What is the role of antibiotics in the treatment of cholera — are they first-line, adjunctive, or indicated only in specific cases? What is the drug, dose, and duration of choice for an adult and for a pregnant woman?
  4. [IM16.6] How do you clinically distinguish dysentery (blood/mucus in stool + fever + tenesmus) from secretory watery diarrhoea (no blood, large volume, afebrile), and why does this distinction change management — specifically, why is loperamide contraindicated in dysentery?
  5. [IM16.15] What are the distinguishing features of Ulcerative Colitis versus Crohn's disease on colonoscopy and histology, and why does this distinction matter for surgical management (curative colectomy in UC vs non-curative resection in Crohn's)?
  6. [IM16.16] What is the step-up treatment ladder for moderate-to-severe Ulcerative Colitis, and which mandatory pre-treatment investigation must be performed before initiating anti-TNF therapy (infliximab) in an Indian patient — and why?