CASE STUDY 2

  Figure 2 labeling. Top left: Pen mic=1ug/ml. Top right:  Cefotaxime mic=1ug/ml. Middle left: Optochin. Lower left: Erythromicin. Lower right: TMP/SMX

The patient was a 70-year-old female who 1 year previously was diagnosed with multiple myeloma. She had been treated with five cycles of immunosuppressive drugs including prednisone, with the last cycle completed 6 weeks previously. The patient presented with a 2-day history of dyspnea and a cough productive of white phlegm. She denied hemoptysis, night sweats, fever, chills, abdominal pain, nausea, vomiting, or chest pain. On physical examination, she had a fever of 38.8 C, pulse of 120/min, and respiratory rate of 20/min. Chest auscultation was significant for bilateral crackles with expiratory wheezes. Chest radiograph showed bilateral, diffuse pulmonary infiltrates with effusion. White blood cell count was 1,700 cells per l. She had a pO₂ of 38 mm Hg which was corrected by receiving oxygen by nasal cannula. Two sets of blood cultures were obtained, and she was begun on cefotaxime and clindamycin intravenously for presumed bacterial pneumonia. Gram stain of the organism recovered from blood is shown in Fig. 1. Susceptibility and optochin testing of the isolate is shown in Fig. 2.

What is the organism causing this patient's infection?

What risk factors does this woman possess for developing infection with this organism?

How do you interpret her susceptibility test results (Fig. 2)? What characteristic does this organism possess which accounts for the penicillin and cefotaxime susceptibility results?

Discuss the epidemiology of organisms with the antibiogram seen in Fig. 2.

What is the major virulence factor for this organism and its role in the pathogenesis of disease?

What other populations are at risk for infection with this organism? What can be done to try to prevent infections with it?

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