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MI7.1-5 | Respiratory Tract Infections — PBL Case

CLINICAL SETTING

A Community Health Officer from the Integrated Tribal Development Agency (ITDA) in Araku Valley, Andhra Pradesh, alerts the district NTEP officer about a cluster of persistent cough illness among residents of Kondapalli hamlet (population ~130). Three adults have been symptomatic for more than 3 weeks. The hamlet is 12 km from the nearest Primary Health Centre (PHC), accessible only by a rough forest track. The area has a history of silicosis among male miners. A mobile ASHA worker conducts a preliminary survey and identifies 8 adults with cough >2 weeks, 2 children under 5 with wheeze and intermittent fever, and one 42-year-old ex-miner, Ramaiah, who has haemoptysis and significant weight loss over 3 months. No household in the hamlet has access to running water. The ASHA records that Ramaiah shares a one-room dwelling with his wife and three children.

Trigger 1: The Index Case Reaches the PHC

Ramaiah is transported by auto-rickshaw to the PHC. On examination: weight 47 kg (usual 58 kg), temperature 37.8°C, RR 22/min, SpO2 93% on room air. There are crackles and dullness on percussion at the right upper zone. The PHC medical officer collects a spot sputum sample and two early-morning samples. The ASHA worker confirms Ramaiah has not previously received any anti-TB treatment. The spot sputum CBNAAT (Xpert MTB/RIF) result returns: 'MTB DETECTED — HIGH' and 'RIF RESISTANCE DETECTED.'

DISCUSSION POINTS

  • What does 'RIF RESISTANCE DETECTED' on Xpert MTB/RIF mean in terms of the rpoB gene, and why does rifampicin resistance serve as a surrogate marker for MDR-TB in the NTEP context?
  • What is the NTEP programmatic action that must occur within 24 hours of this Xpert result? Who must be notified, and what forms must be filled?
  • Ramaiah's two early-morning sputum samples are also sent for LPA (Line Probe Assay). What additional drug resistances can LPA detect that Xpert cannot, and what is the turnaround time?
Click to reveal Trigger 2: Contact Tracing and Household Investigations (discuss previous trigger first!)

Trigger 2: Contact Tracing and Household Investigations

The district NTEP officer activates contact tracing. Ramaiah's wife, Sarojini (38 years), is found to have a 6-week history of dry cough and mild fever; her Mantoux test shows 14 mm induration. She received BCG at birth (scar visible). Their eldest child, Govind, 14 years, has no symptoms and a Mantoux of 8 mm. The youngest child, Parvati, 4 years, is febrile with a persistent cough for 3 weeks; her chest X-ray shows bilateral hilar lymphadenopathy. Parvati's Xpert MTB/RIF on nasopharyngeal aspirate is 'MTB DETECTED — LOW.' Among the miners in the hamlet, two are found to have bilateral upper lobe fibrotic lesions with scattered calcified nodules on CXR — radiological features consistent with silico-tuberculosis.

DISCUSSION POINTS

  • Sarojini is BCG-vaccinated and has a 14 mm Mantoux. How would you interpret this result? Would you recommend an IGRA (QuantiFERON) for her, and what specific advantage does IGRA have over Mantoux in a BCG-vaccinated individual? What is NTEP's current recommendation for LTBI treatment in household contacts of MDR-TB index cases?
  • Parvati has bilateral hilar lymphadenopathy with low-grade Xpert positivity. How does paediatric pulmonary TB differ in clinical and microbiological presentation from adult post-primary TB? Why is sputum culture essential even when Xpert is positive in a child?
  • What is silico-tuberculosis, and how does silica dust exposure alter macrophage function to increase TB susceptibility? How does this change the clinical management and NTEP notification requirements for the two miners?
Click to reveal Trigger 3: Treatment Initiation, Drug Resistance Pattern, and Infection Control (discuss previous trigger first!)

Trigger 3: Treatment Initiation, Drug Resistance Pattern, and Infection Control

LPA results for Ramaiah: resistant to Isoniazid (inhA mutation) and Rifampicin (rpoB mutation); sensitive to fluoroquinolones, bedaquiline, and second-line injectables. He is enrolled in the NTEP shorter MDR-TB treatment regimen. The PHC lacks an isolation room. Sarojini is started on Isoniazid Preventive Therapy (IPT). The district NTEP officer arranges a community meeting to address stigma and provide counselling. However, during the second month of treatment, Ramaiah becomes increasingly dyspnoeic; an audiogram reveals sensorineural hearing loss bilaterally. A review of his regimen shows he received an injectable agent in the intensive phase.

DISCUSSION POINTS

  • Name all components of the NTEP 9-month shorter MDR-TB regimen (intensive and continuation phases), and explain which component of Ramaiah's regimen most likely caused the sensorineural hearing loss. How should the regimen be modified?
  • What infection control measures should be implemented in this one-room dwelling to reduce transmission to Sarojini, Parvati, and Govind? Address both natural ventilation principles and N95/surgical mask allocation in the resource-limited setting.
  • Ramaiah's inhA mutation confers resistance to Isoniazid but he is prescribed 'high-dose Isoniazid' as part of the shorter regimen. Explain the pharmacological rationale: why is high-dose INH retained despite inhA-mediated resistance? What is the difference between katG and inhA mutations in terms of INH MIC and clinical significance?

Group Task Assignments

Group 1: Molecular Diagnostics and Drug Resistance Mechanisms

  • Prepare a flowchart of the NTEP diagnostic algorithm from sputum collection → Xpert → LPA → culture, including turnaround times and decision points at each step.
  • Compare katG vs inhA mutations: resistance level (MIC), cross-resistance to ethionamide, and implications for regimen choice in MDR-TB.

Competencies: MI7.2, MI7.5

Group 2: Paediatric TB and Contact Tracing

  • Create a table comparing adult post-primary TB vs paediatric primary TB: clinical features, radiological patterns, specimen types, smear positivity rates, and NTEP treatment algorithm.
  • Design a contact tracing action plan for Kondapalli hamlet covering: household contacts, extended community contacts, LTBI screening criteria, and eligibility for IPT vs preventive therapy for MDR-TB contacts.

Competencies: MI7.2, MI7.3

Group 3: Occupational Risk and Silico-TB

  • Summarise how silica particle phagocytosis impairs macrophage killing of MTB (lysosome disruption, impaired phagosome-lysosome fusion, NLRP3 inflammasome dysregulation).
  • Identify the additional regulatory obligations under NTEP and Occupational Health guidelines when TB occurs in a silica-exposed worker — reporting, compensation, and employer notification.

Competencies: MI7.2, MI7.3

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [MI7.2] What is the mechanism by which rpoB gene mutations cause rifampicin resistance in M. tuberculosis, and why is this a proxy marker for MDR-TB in the NTEP algorithm?
  2. [MI7.2] What are the components and sequencing of the NTEP 9-month shorter MDR-TB regimen (2BLHZEC + 7BLHzE), and what is the rationale for retaining high-dose isoniazid despite inhA resistance?
  3. [MI7.2] How does silica dust impair macrophage-mediated killing of MTB, and what is the clinical significance of silico-tuberculosis in the NTEP context?
  4. [MI7.5] What are the NTEP criteria for sputum quality before processing for CBNAAT and LPA? What alternative specimens are used in paediatric TB where sputum cannot be obtained?
  5. [MI7.3] How does bilateral hilar lymphadenopathy in a child differ from adult-type upper lobe cavitary disease in terms of TB pathogenesis (primary vs post-primary), and what are the microbiological implications for specimen collection and sensitivity of diagnostic tests?
  6. [MI7.2] What is the NTEP programmatic response (notification, enrolment, counselling, IPT allocation) within 24 hours of an Xpert MTB/RIF result showing MTB detected with RIF resistance?