I had PCP last year and it's really vile. I was told that it was commonly known in the HIV community as the "great finisher". I became intollerent to Septrin towards the end of my 21 day treatment (fragmented red blood cells and platelet collapse) and had several months of pentamadine. About to start prophylactic pentamadine again after wegs re-diagnosis. I'd really like not to have PCP again.
PCP is caused by a fungus which is commonly found in healthy human lungs, but which can become the agent of disease in people with weakened immune systems. I'm not sure that there's a great deal you cann do in our situation to avoid it, other than acting quickly and determinedly as norcalian did.