Page 9 of 10
MI9.1-6 | Zoonotic, Opportunistic & Emerging Infections — Case Study
CLINICAL SCENARIO
In August 2024, the District Surveillance Officer of Thanjavur, Tamil Nadu reported a cluster of 14 febrile illness cases with jaundice and acute kidney injury among paddy farmers within 10 days of severe flooding. The district health team suspected a zoonotic outbreak and initiated a field investigation. You are a third-year MBBS student attached to the Community Medicine department who has been asked to assist with the outbreak investigation report.
Instructions
Scenario: Fourteen paddy farmers (ages 22–58) from three adjacent villages in Thanjavur district, Tamil Nadu, were hospitalised between 12–22 August 2024 following severe monsoon flooding. All reported wading through floodwaters for 3–8 days during harvest. Clinical features included: high fever (>39°C), severe headache, myalgia, conjunctival suffusion, jaundice (8/14), oliguria (6/14), and haemorrhagic manifestations (3/14). Two patients died. Rodent population surveys showed a 5-fold increase in rat sightings post-flooding.
Using your knowledge of Microbiology (MI9.1, MI9.3), Community Medicine surveillance principles, and the One Health framework, write a structured outbreak investigation report addressing the sections below.
Length: 600-800 words
What to Submit
Section 1: Epidemiological Assessment and Case Definition (100–150 words)
Define a 'probable case' and a 'confirmed case' of leptospirosis in this outbreak context. Identify the most likely source, mode of transmission, and explain why the August monsoon timing and flood exposure are relevant to the epidemiological pattern.
Guidance: Use standard WHO outbreak case definition structure. Include the occupation, exposure route, and clinical feature criteria. Link the monsoon season, rodent density, and floodwater contamination to Leptospira survival.
Section 2: Microbiological Investigation Plan (150–200 words)
Outline the microbiological investigations you would order for the hospitalised patients and explain the timing and rationale for each test. Include at least three different diagnostic modalities used at different stages of illness.
Guidance: Consider: (a) dark-field microscopy on blood/urine in first week; (b) culture on EMJH/Fletcher's media (up to 4 weeks); (c) MAT (reference standard, Week 2+); (d) IgM ELISA (from Day 5–7). For each test: state the specimen, timing, and what a positive result means.
Section 3: Analysis of Severe Leptospirosis (Weil's Disease) (100–150 words)
Six patients developed acute kidney injury with oliguria. Explain the pathogenesis of renal involvement in severe leptospirosis (Weil's disease). What haematological findings would you expect on investigation and what do they represent?
Guidance: Discuss direct renal tubular injury (Leptospira antigen deposition in tubules → acute tubular necrosis), immune complex deposition, and hepatic involvement. For haematology: thrombocytopaenia, elevated CRP/ESR, anaemia, and elevated CPK.
Section 4: Public Health Response and One Health Intersections (150–200 words)
Propose a public health response for this outbreak that addresses the immediate clinical response, the animal/environmental reservoir, and long-term prevention under the One Health framework. Include the role of the National Programme for Prevention & Control of Leptospirosis.
Guidance: Immediate: report to IDSP (P-form), case management with doxycycline/penicillin. Environmental: rodent control, floodwater drainage, PPE for rescue workers. Community: chemoprophylaxis (doxycycline 200 mg weekly) for at-risk workers. Long-term: vaccination of livestock, rodent population management, surveillance. Mention the National Leptospirosis Control Programme and IDSP integration.
Grading Rubric — Zoonotic Outbreak Investigation Rubric (20 points)
| Criterion | Points | Full-marks descriptor |
|---|---|---|
| Case Definition and Epidemiological Analysis (MI9.1, MI9.3) | 5 pts | Clear probable and confirmed case definitions using WHO format; accurately identifies occupational/flood exposure as transmission route; explains monsoon seasonality and rodent density link to contaminated floodwater with mechanistic clarity. |
| Microbiological Investigation Plan with Timing and Rationale (MI9.3) | 5 pts | Describes ≥3 diagnostic tests (DFM, EMJH/Fletcher's culture, IgM ELISA, MAT) with correct specimen type, timing relative to illness day, and interpretation of positive results; understands the diagnostic window of each test. |
| Pathogenesis of Weil's Disease and Laboratory Correlation (MI9.1, MI9.2) | 5 pts | Accurately explains renal tubular injury (direct Leptospira toxin + immune complex deposition → ATN); correctly interprets haematological findings (thrombocytopaenia, elevated creatinine/bilirubin/CK); links clinical severity to pathogenic serovar. |
| Public Health Response and One Health Integration (MI9.6) | 5 pts | Structured immediate + medium + long-term response; correct use of IDSP reporting (P-form/S-form); mentions National Leptospirosis Control Programme; integrates One Health (animal surveillance, environmental management, human health) with specific interventions for each domain. |
PEER REVIEW
Review your peer's outbreak investigation report using the four rubric criteria. For each criterion: (1) identify one specific strength with a textual example, (2) identify one specific gap or error with suggested improvement. Conclude with an overall assessment of whether the report demonstrates readiness to participate in a real district-level outbreak investigation. Your review should be 200–300 words, constructive, and specific — avoid generic praise.