Medical Microbiology and Infection

at a Glance

Fourth EditionStephen Gillespie and Kathleen Bamford

Case Studies

Case 10

A 52-year-old dialysis patient of Somalian origin who has been in the UK for 10 years presents with a 2 month history of night sweats, intermittent fever, weight loss and lumbar pain. You suspect tuberculosis.

  • 1. What investigations will you carry out to confirm this diagnosis?

    Chest X-ray, MRI spine, microscopy and culture of sputum and early morning urine for acid-fast bacteria. Tests for immune response to mycobacteria (tuberculin skin test or IGRA). Total and differential white cell count and C-reactive protein to monitor treatment.

  • 2. What aspects of this patient's history suggest an increased risk of tuberculosis?

    Patients who are born in developing countries, particularly sub-Saharan Africa and Asia, are likely to have been exposed to tuberculosis in childhood. Clinical tuberculosis is more likely in dialysis patients.

  • 3. What is the pathogenesis of clinical tuberculosis?

    Primary infection (usually in childhood in endemic areas) is usually acquired by inhalation, which causes a primary focus in the lung with associated lymphadenopathy. This usually heals with scaring of the primary focus but may disseminate to cause miliary tuberculosis with or without meningitis. Later, usually when the immune response is compromised (e.g. due to steroids, immunosuppressive therapy, malnutrition or dialysis), reactivation can occur, associated with caseous necrosis in the involved tissues (most commonly the lung) and regional lymphadenopathy.

  • 4. What imaging findings would support a diagnosis of tuberculosis in this case?

    Upper or mid-zone consolidation and or cavitation, and hilar lymphadenopathy on the chest X-ray and necrosis of the intervertebral disc with bony erosion on MRI of the spine would all be consistent with tuberculosis in the lung and spine respectively.

  • 5. Direct examination of sputum from this patient reveals acid- and alcohol-fast bacilli. What management should be instigated?

    This indicates "smear-positive" infection with a risk of spread. The patient should be nursed in a negative-pressure side room and healthcare staff should wear personal protective respiratory masks when attending to the patient's needs. The patient is considered infectious for the first 2 weeks of therapy, which should be with quadruple antituberculous agents for 2 months, followed by dual therapy for 10 months. The total period of treatment is extended from 6 to 12 months because of bone involvement. The patient should be referred to a specialist microbiology/infectious disease team for management.

  • 6. Are there public health issues that need to be addressed?

    Yes. Part of the management of tuberculosis, especially for smear-positive infections, is the measures taken to trace contacts and screen them for infection. This can be done by a combination of tuberculin skin test/IGRA and chest X-ray. Prophylaxis or treatment can then be given as needed.

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