I would not run too quick to have PCR performed without having some background analysis done first, especially in the area of microbiology and immunology.
There are many other factors at work which can have the end result being parasitic infection[s].
A good example is AIDS albeit an extreme example. AIDS patients will end up with multiple infections due to failing T cell production and overall immune system failure.
If you have a condition that is suppressing one or more functions of the immune system through a "stealth" infection or autoimmune dysfunction,{for eg.} parasitic infections can and do surface.
Having the identification of the organism in this case, could mislead the course of treatment, and even exasperate the problem. Shroom