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 for immunocompromised individuals
prophylaxis with co-trimoxazole or regular pentamidine inhalations may help prevent PCP.
clinical picture
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