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RE: Yersinia IgG and IgA, IgA has been shown to correlate with Reactive Arthritis (which can be triggered by Yersinia). Some people (KDM included) think this is because the patient is still infected, since IgA doesn't last in the body very long (apparently). Since this is negative in your case, I believe KDM suspects that another infection (an active one) is to blame for your symptoms (or at least some of them).
I just thought about the first paper again, and I don't really get it...doesn't sensitivity in this case mean how often it is found in patients with bacterial infection? If not, I apologise.
Ah, thanks for pointing that out...re: TB, I was trying to think of a chronic bacterial infection that isn't controversial. As for local infection, is the lung unique in this case, or would you expect any local infection to show similarly low levels of CRP?
re: IgA, I was just repeating what I've read, and in the study I posted before with the IF of Yersinia antigens, both the IgA and IgG levels decreased with antibiotic treatment (in a matter of months).