title: Follow-up of 686 patients with acute Q fever and detection of chronic infection.
abstract: BACKGROUND
  Recent outbreaks in the Netherlands allowed for laboratory follow-up of a large series of patients with acute Q fever and for evaluation of test algorithms to detect chronic Q fever, a condition with considerable morbidity and mortality.
  
  
  METHODS
  For 686 patients with acute Q fever, IgG antibodies to Coxiella burnetii were determined using an immunofluorescence assay at 3, 6, and 12 months of follow-up. Polymerase chain reaction (PCR) was performed after 12 months and on earlier serum samples with an IgG phase I antibody titer ≥ 1:1024.
  
  
  RESULTS
  In 43% of patients, the IgG phase II antibody titers remained high (≥ 1:1024) at 3, 6, and 12 months of follow-up. Three months after acute Q fever, 14% of the patients had an IgG phase I titer ≥ 1:1024, which became negative later in 81%. IgG phase I antibody titers were rarely higher than phase II titers. Eleven cases of chronic Q fever were identified on the basis of serological profile, PCR results, and clinical presentation. Six of these patients were known to have clinical risk factors at the time of acute Q fever. In a comparison of various serological algorithms, IgG phase I titer ≥ 1:1024 at 6 months had the most favorable sensitivity and positive predictive value for the detection of chronic Q fever.
  
  
  CONCLUSIONS
  The wide variation of serological and PCR results during the follow-up of acute Q fever implies that the diagnosis of chronic Q fever, necessitating long-term antibiotic treatment, must be based primarily on clinical grounds. Different serological follow-up strategies are needed for patients with and without known risk factors for chronic Q fever.
authors.affiliation: Epidemiology and Surveillance Unit, Center for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands. wim.van.der.hoek@rivm.nl
authors.forename: Wim
authors.initials: W
authors.lastname: van der Hoek
authors.forename: Bart
authors.initials: B
authors.lastname: Versteeg
authors.forename: Jamie C E
authors.initials: JC
authors.lastname: Meekelenkamp
authors.forename: Nicole H M
authors.initials: NH
authors.lastname: Renders
authors.forename: Alexander C A P
authors.initials: AC
authors.lastname: Leenders
authors.forename: Ineke
authors.initials: I
authors.lastname: Weers-Pothoff
authors.forename: Mirjam H A
authors.initials: MH
authors.lastname: Hermans
authors.forename: Hans L
authors.initials: HL
authors.lastname: Zaaijer
authors.forename: Peter C
authors.initials: PC
authors.lastname: Wever
authors.forename: Peter M
authors.initials: PM
authors.lastname: Schneeberger
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000907:Antibodies, Bacterial / Q000097:blood*; D002908:Chronic Disease; D019411:Clinical Laboratory Techniques / Q000379:methods*; D016997:Coxiella burnetii / Q000276:immunology*; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods; D005500:Follow-Up Studies; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D016133:Polymerase Chain Reaction / Q000379:methods; D011778:Q Fever / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D012680:Sensitivity and Specificity
chemical_list: D000907:Antibodies, Bacterial; D007074:Immunoglobulin G