Pneumocystis

CASE 1

• A 35 year old man was diagnosed with HIV 3 years earlier. He began prophylactic antimicrobial therapy at that time but has since been lost to follow-up and has been using only herbal medications. He now comes to the clinic with a history of fevers and increasing dry cough for the past 2 weeks. He has no shaking chills, urinary or gastrointestinal complaints, and no rash. However, he has noticed increasing shortness of breath with mildly vigorous phycial activity.

• On physical examination, his temperature is 38.4 degrees. The lungs fields are clear to percussion and auscultation. The remainder of the examination is signficant only for mild oral thrush.

• The complete bloos count was unremarkable. the WBC count was 7,800 with a normal differential count. A CD4 lymphocyte count was 75/mm3. The patient has an oxygen saturation (measured by an oximetry placed over one of his fingernails) of 92%. However, after walking up and down a flight of stairs, his O2 saturation drops to 83%. A chest radiograph reveals reticulonodular densities in both lung bases.

• The patient is induced to produce sputum by inhaling nebulized normal saline. A sample is obtained and sent for silver staining. The smear shows numerous small cysts with internal polynuclear structures and the appearance of partially crushed ping-pong balls, consistent with Pneumocystis jiroveci.

• The patient is treated with a 3-week course of high-dose co-trimoxazole. His fever and cough resolve slowly. At the end of therapy, he is placed on a daily dose of co-trimoxazole indefinitely and referred for antiretroviral therapy.

Questions:

1. How did the patient acquire this infection?
2. What would have been the outcome of his exposure had he been HIV-negative?
3. How can you tell if this patient is at risk for this infection? What laboratory measurement correlates with risk of pneumocystis pneumonia (PCP)?
4. What would you expect to see if you took a biopsy of the lung tissue that is relatively opaque on the chest radiograph? Does this explain the dyspnea and oxygen desaturation on exertion?
5. Why was the WBC count normal?
6. Confirming a diagnosis this case was very lucky. What are some other ways to detect this infection in the laboratory? Would you like to obtain sputum for culture?
7. Co-trimoxasole wokred well in this case. What other therapeutic options are there?
8. Can this patient ever stop taking co-trimoxasole? If so, what would the circumstances be?