Early Diagnosis and Treatment of Patients with Symptomatic Acute Q Fever Do Not Prohibit IgG Antibody Responses to Coxiella burnetii

Little is known about the effect of timing of antibiotic treatment on development of IgG antibodies following acute Q fever. We studied IgG antibody responses in symptomatic patients diagnosed either before or during development of the serologic re-sponse to Coxiella burnetii. Between 15 and 31May 2009, 186 patients presented with acute Q fever, of which 181 were included in this retrospective study: 91 early-diagnosed (ED) acute Q fever patients, defined as negative IgM phase II enzyme-linked im-munosorbent assay (ELISA) and positive PCR, and 90 late-diagnosed (LD) acute Q fever patients, defined as positive/dubious IgM phase II ELISA and positive immunofluorescence assay (IFA). Follow-up serology at 3, 6, and 12 months was performed us-ing IFA (IgG phase I and II). High IgG antibody titers were defined as IgG phase II titers of>1:1,024 together with IgG phase I titers of>1:256. At 12 months, 28.6 % of ED patients and 19.5 % of LD patients had high IgG antibody titers (P 0.17). No statis-tically significant differences were found in frequencies of IgG phase I and IgG phase II antibody titers at all follow-up appoint-ments for adequately and inadequately treated patients overall, as well as for ED and LD patients analyzed separately. Addition-ally, no significant difference was found in frequencies of high antibody titers and between early (treatment started within 7 days after seeking medical attention) and late timing of treatment. This study indicates that early diagnosis and antibiotic treatment of acute Q fever do not prohibit development of the IgG antibody response