Overview
Pneumocystis jirovecii was previously thought to be a protozoan but is more closely related to fungi. It was previously known as Pneumocystis carinii, hence the abbreviation ‘PCP’ for Pneumocystis pneumonia. It is found widely in nature.
PCP is the most common opportunistic infection in people with acquired immunodeficiency syndrome (AIDS). Since it is seen when CD4+ T-cell counts are <200 cells/mm3, PCP prophylaxis should be given to people with CD4+ counts of <200 cells/mm3.
Pathophysiology
Once inhaled, it attaches to alveoli and proliferates. Impaired T-cell immunity can lead to uncontrolled proliferation and infection, which can lead to fibrosis and oedema.
Risk Factors
- Immunodeficiency – HIV or other immunodeficiencies
- Immunosuppression – including glucocorticoids and other immunosuppressive drugs
- Protein malnutrition
Presentation
Features of Pneumocystis pneumonia tend to present insidiously over days/weeks and can include:
- Dyspnoea
- Dry cough
- Reduced exercise tolerance
- Exercise-induced hypoxia
- Chest signs are uncommon, crackles may be seen in some people
- Extrapulmonary manifestations are rare (~1%) and can include hepatomegaly, splenomegaly, lymphadenopathy, and choroid lesions
Investigations
Overview
Some investigations include:
- Chest X-ray – may show bilateral interstitial infiltrates, lobar consolidation, or may be normal
- High-resolution CT chest – may show diffuse ground-glass opacification
- Sputum culture – not very effective at identifying PCP
- Bronchoalveolar lavage – silver stain shows cysts associated with PCP
Management
Overview
Management involves the use of co-trimoxazole and intravenous pentamidine in severe cases. Corticosteroids may be used if hypoxic and can reduce the risk of respiratory failure.
