Pneumocystis (carinii) jirovecii pneumonia (PCP)

introduction

Pneumocystis jirovecii is a yeast-like fungus which is specifically pathogenic to humans and is commonly found in the lungs of normal humans.
> 75% of children are seropositive by the age of 4.
it may cause a fulminant bilateral pneumonia in those who are immunocompromised such as those on cytotoxics or immunosuppressants for treatment of cancer, or those with AIDS for which it is an AIDS-defining illness.
infection is also common in infants with hyper IgM syndrome, an X-linked or autosomal recessive trait
it is important for the clinician to consider as antibiotic treatment differs to the usual regime for pneumonia, and it may rapidly progress to a fatal outcome, although usually after a subacute initial onset.
the PCP acronym comes from when the organism was previous known as Pneumocystis carinii, but this name as now used for the organism found in rats.

prophylaxis with co-trimoxazole or regular pentamidine inhalations may help prevent PCP.

usually has subacute onset
fever
tachycardia
cough
SOB
chest pains
often hypoxia out of proportion to CXR findings
characteristic CXR findings:
- most patients have diffuse bilateral infiltrates extending from the perihilar region which may appear as bilateral lower lobe consolidation
- CXR may be normal in up to 40% of patients, particularly early in the course
propensity to develop a pneumothorax
Acute Respiratory Distress Syndrome (ARDS) may develop in fulminant cases

microscopy of sputum shows characteritic cysts which unlike Histoplasma or Cryptococcus, form aggregates of 2 to 8.
NB. PCR is not helpful as most people have this organism as a commensal

supportive care as per usual
steroids to prevent delayed inflammation and worsening of condition 4 days post-Rx
antibiotics for 21 days such as:
- co-trimoxazole
- pentamidine
- clindamycin
intubation is generally required for severe cases which develop Acute Respiratory Distress Syndrome (ARDS)