Pneumocystis pneumonia (PCP)
Pneumocystis jirovecii (previously known as Pneumocystis carinii) causes pneumonia and disseminated illness in imunocompromised patients.
Pneumocystis jirovecii is described as a fungus however it was originally thought to be a protozoan due to its existence as cysts, sporozoites and trophozoites. The reservoir for infection is thought to be animals, with aerosol spread. Clinical pneumonia is thought to be a reactivation of latent infection. The risk of pneumonia increases as the CD4 count falls, it is rare until the count drops below 200 cells/mm3.
Gradual onset of non-specific symptoms of anorexia and fatigue followed by dyspnoea, non-productive cough, lowgrade fever and tachypnoea. On auscultation there may be fine crackles or breath sounds may be normal.
Chest X-ray: The typical features are diffuse bilateral ground glass infiltrates progressing to widespread consolidation in severe cases (sparing of the costophrenic angles and apices).
Bronchoalveolar lavage reveals trophozoites & cysts on silver stain or immunofluorescence.
Intravenous high dose cotrimoxazole (3 week regimen). In significant hypoxia steroids are used, patients may require CPAP or mechanical ventilation. Patients with HIV require prophylaxis with cotrimoxazole or monthly nebulised pentamidine if they have a CD4 count of less than 0.2 × 109/L, an AIDS defining illness or following an previous episode of PCP.
90% of patients with a first episode respond to treatment and survive. Failure to respond or development of respiratory failure has significant mortality.