title: Chlamydia psittaci: a relevant cause of community-acquired pneumonia in two Dutch hospitals.
abstract: BACKGROUND
  Of all hospitalised community-acquired pneumonias (CAPs) only a few are known to be caused by Chlamydia psittaci. Most likely the reported incidence, ranging from of 0% to 2.1%, is an underestimation of the real incidence, since detection of psittacosis is frequently not incorporated in the routine microbiological diagnostics in CAP or serological methods are used.
  
  
  METHODS
  C. psittaci real-time polymerase chain reaction (PCR) was routinely performed on the sputum of 147 patients hospitalised with CAP, who participated in a clinical trial conducted in two Dutch hospitals. In 119/147 patients the paired complement fixation test (CFT) was also performed for the presence of Chlamydia antibodies. Positive CFTs were investigated by micro- Immunofluorescence for psittacosis specificity. Case criteria for psittacosis were a positive PCR or a fourfold rise of antibody titre in CFT confirmed by micro- Immunofluorescence. Furthermore, we searched for parameters that could discriminate psittacosis from CAPs with other aetiology.
  
  
  RESULTS
  7/147 (4.8%) patients were diagnosed with psittacosis: six with PCR and one patient with a negative PCR, but with CFT confirmed by micro- Immunofluorescence. Psittacosis patients had had a higher temperature (median 39.6 vs. 38.2 °C;) but lower white blood cell count (median 7.4 vs. 13.7 x 109/l) on admission compared with other CAP patients.
  
  
  CONCLUSIONS
  In this study, C. psittaci as CAP-causing pathogen was much higher than previously reported. To detect psittacosis, PCR was performed on all CAP patients for whom a sputum sample was available. For clinical use, PCR is a fast method and sputum availability allows genotyping; additional serology can optimise epidemiological investigations.
authors.affiliation: Department of Internal Medicine, St. Antonius Hospital, Nieuwegein, the Netherlands.
authors.forename: S M C
authors.initials: SM
authors.lastname: Spoorenberg
authors.forename: W J W
authors.initials: WJ
authors.lastname: Bos
authors.forename: E J
authors.initials: EJ
authors.lastname: van Hannen
authors.forename: F
authors.initials: F
authors.lastname: Dijkstra
authors.forename: E R
authors.initials: ER
authors.lastname: Heddema
authors.forename: H
authors.initials: H
authors.lastname: van Velzen-Blad
authors.forename: R
authors.initials: R
authors.lastname: Heijligenberg
authors.forename: J C
authors.initials: JC
authors.lastname: Grutters
authors.forename: B M
authors.initials: BM
authors.lastname: de Jongh
mesh_terms: D000368:Aged; D000907:Antibodies, Bacterial / Q000032:analysis; D002691:Chlamydophila psittaci / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000382:microbiology*; D004269:DNA, Bacterial / Q000032:analysis; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D011014:Pneumonia / Q000453:epidemiology / Q000382:microbiology*; D009956:Psittacosis / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology*; D013183:Sputum / Q000382:microbiology
chemical_list: D000907:Antibodies, Bacterial; D004269:DNA, Bacterial