title: Long-Term Serological Follow-Up of Acute Q-Fever Patients after a Large Epidemic.
abstract: BACKGROUND
  Serological follow-up of acute Q-fever patients is important for detection of chronic infection but there is no consensus on its frequency and duration. The 2007-2009 Q-fever epidemic in the Netherlands allowed for long-term follow-up of a large cohort of acute Q-fever patients. The aim of this study was to validate the current follow-up strategy targeted to identify patients with chronic Q-fever.
  
  
  METHODS
  A cohort of adult acute Q-fever patients, diagnosed between 2007 and 2009, for whom a twelve-month follow-up sample was available, was invited to complete a questionnaire and provide a blood sample, four years after the acute episode. Antibody profiles, determined by immunofluorescence assay in serum, were investigated with a special focus on high titres of IgG antibodies against phase I of Coxiella burnetii, as these are considered indicative for possible chronic Q-fever.
  
  
  RESULTS
  Of the invited 1,907 patients fulfilling inclusion criteria, 1,289 (67.6%) were included in the analysis. At any time during the four-year follow-up period, 58 (4.5%) patients were classified as possible, probable, or proven chronic Q-fever according to the Dutch Q-fever Consensus Group criteria (which uses IgG phase I ≥1:1,024 to as serologic criterion for chronic Q-fever). Fifty-two (89.7%) of these were identified within the first year after the acute episode. Of the six patients that were detected for the first time at four-year follow-up, five had an IgG phase I titre of 1:512 at twelve months.
  
  
  CONCLUSIONS
  A twelve-month follow-up check after acute Q-fever is recommended as it adequately detects chronic Q-fever in patients without known risk factors. Additional serological and clinical follow-up is recommended for patients with IgG phase I ≥1:512, as they showed the highest risk to progress to chronic Q-fever.
authors.affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, 's-Hertogenbosch, the Netherlands; Centre for Infectious Disease Control, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Cornelia C H
authors.initials: CC
authors.lastname: Wielders
authors.affiliation: Academic Collaborative Centre AMPHI, Department of Primary and Community Care, Radboud university medical center (Radboudumc), Nijmegen, the Netherlands.
authors.forename: Joris A F
authors.initials: JA
authors.lastname: van Loenhout
authors.affiliation: Academic Collaborative Centre AMPHI, Department of Primary and Community Care, Radboud university medical center (Radboudumc), Nijmegen, the Netherlands; Department of Infectious Disease Control, Municipal Health Service (GGD) Hart voor Brabant, 's-Hertogenbosch, the Netherlands.
authors.forename: Gabriëlla
authors.initials: G
authors.lastname: Morroy
authors.affiliation: Department of Infectious Disease Control, Municipal Health Service (GGD) Hart voor Brabant, 's-Hertogenbosch, the Netherlands.
authors.forename: Ariene
authors.initials: A
authors.lastname: Rietveld
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Daan W
authors.initials: DW
authors.lastname: Notermans
authors.affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, 's-Hertogenbosch, the Netherlands.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Wever
authors.affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, 's-Hertogenbosch, the Netherlands.
authors.forename: Nicole H M
authors.initials: NH
authors.lastname: Renders
authors.affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, 's-Hertogenbosch, the Netherlands.
authors.forename: Alexander C A P
authors.initials: AC
authors.lastname: Leenders
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Wim
authors.initials: W
authors.lastname: van der Hoek
authors.affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, 's-Hertogenbosch, the Netherlands; Centre for Infectious Disease Control, National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Schneeberger
mesh_terms: D000328:Adult; D000907:Antibodies, Bacterial / Q000097:blood; D016997:Coxiella burnetii / Q000276:immunology; D058872:Epidemics; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D011778:Q Fever / Q000097:blood* / Q000453:epidemiology / Q000276:immunology; D011795:Surveys and Questionnaires
chemical_list: D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D007075:Immunoglobulin M