Immuno-PCR for the early serological diagnosis of acute infectious diseases: the Q fever paradigm

To reduce the delay in diagnosis of Q fever, we have adapted the ultrasensitive immuno-PCR method for the detection of Phase II IgM anti-Coxiella burnetii. We compared its performance to ELISA, IFA and PCR using 31 acute Q fever sera and 50 control sera. The best sensitivity was obtained by iPCR (27 out of 31) followed by PCR (18 out of 31), ELISA (12 out of 31) and IFA (10 out of 31). A specificity of 92% was found by iPCR (3 false positive out of 40), 92% for ELISA (3 false positive out of 40) whereas PCR and IFA exhibited a specificity of 100%. Among the 31 Q fever sera, we compared the four methods for the detection of the early sera sampled during the two first weeks after the onset of symptoms and found a sensitivity of 90% by iPCR, 55% for PCR, 35% for ELISA and 25% for IFA. The results presented in this study suggest that iPCR is a promising, sensitive and specific method that can be used for the early diagnosis of acute Q fever and more generally for acute infections where traditional methods lack sensitivity.