Pneumocystis carinii pneumonia

Nowadays Pneumocystis carinii pneumonia most commonly occurs in those at risk of HIV infection who fail to take adequate prophylaxis or in those who are newly diagnosed with advanced disease, where it is frequently the presenting illness.

Chest x ray appearance of Pneumocystis carinii pneumonia showing interstitial infiltrates

Clinical suspicion is aroused early in patients who are under regular medical supervision, leading to earlier diagnosis. Later diagnosis is asssociated with more severe disease and poorer treatment outcome. Techniques of diagnosis include sputum induction with nebulised saline; this obviates the need for bronchoscopy but the diagnostic sensitivity is lower. The use of lavage alone at bronchoscopy avoids transbronchial biopsy with its complications of haemorrhage and pneumothorax. Exercise oximetry and alternative imaging techniques with radiolabelled compounds are also being used in diagnosis. Monoclonal antibodies to pneumocystis proteins and sensitive DNA probes have been developed but have yet to reach the bedside. In the absence of a confirmatory test, a presumptive diagnosis may be made based on the clinical presentation and chest x ray appearances in a patient severely immunosuppressed and at risk.

Prophylaxis for Pneumocystis carinii pneumonia is essential after a first attack (secondary prophylaxis) but is also recommended for all patients once their CD4 cell counts falls below 200×10⁶/l (primary prophylaxis). The risk of a first episode of infection below this CD4 count level in patients not on antiretroviral therapy is estimated to be 18% at 12 months for those who are asymptomatic, rising to 44% for those who have early symptomatic disease (eg oral candida, fever). Co-trimoxazole …