Medical Microbiology and Infection

at a Glance

Fourth EditionStephen Gillespie and Kathleen Bamford

Case Studies

Case 18

A 55-year-old woman who was previously well presents with shortness of breath, fever, and cough productive of sputum. She is a regular smoker and has not travelled abroad recently. Clinical examination reveals that her pulse is 104, her blood pressure 100/60 mmHg and her respiratory rate 32 breaths/minute. A chest X-ray shows extensive consolidation at her lower left base and a small effusion.

  • 1. What is your differential diagnosis?

    This patient is quite ill so although there are a wide range of possible diagnoses one would be most concerned about infection with Streptococcus pneumoniae or Legionella pneumophila.

  • 2. What is the influence of smoking in this story?

    Smoking makes infections more likely and these tend to be associated with a poorer prognosis than in nonsmokers.

  • 3. What further investigations would be helpful?

    All of the other causes of acute community-acquired pneumonia should be considered. Therefore, sputum should be cultured if available and blood cultures taken. A urinary antigen test for Legionella and S. pneumoniae is the quickest way of making a diagnosis of Legionnaires’ disease and supporting the diagnosis of pneumococcal disease. NAAT tests for the other respiratory bacteria should be performed if available. Virological causes should also be investigated, with real-time NAAT tests if available.

  • 4. A diagnosis of community-acquired pneumonia has been made, but what is the most likely pathogen?

    Streptococcus pneumoniae.

  • More info: The patient is treated with ceftriaxone and clarithromycin and there is an initial response to this prescription: her temperature, pulse and respiratory rate fall and she begins to feel better. After 6 days the patient complains that she is feeling worse, and that she is more breathless. The nurses report that her temperature has come back.
  • 5. What complication may have developed?

    The improvement that has occurred suggests that the treatment is effective. In this case a pneumococcus was isolated from initial blood and sputum samples that was fully sensitive to penicillin. The relapse of symptoms should prompt a search for one of the suppurative complications, which could include a pleural empyema or, more rarely, a cardiac empyema.

  • 6. How would you make the diagnosis?

    Careful clinical examination may reveal signs of an empyema.

  • 7. What additional procedure may be required?

    A diagnostic and therapeutic aspirate of the empyema fluid may be helpful.

  • 8. What microbiological examination should be performed now?

    Aspirated pus should be subjected to conventional culture. Additionally the specimen could be examined by specific NAATs or by a 16S NAAT.

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