title: Clinical, laboratory and radiologic characteristics of 2009 pandemic influenza A/H1N1 pneumonia: primary influenza pneumonia versus concomitant/secondary bacterial pneumonia.
abstract: BACKGROUND
  Although influenza virus usually involves the upper respiratory tract, pneumonia was seen more frequently with the 2009 pandemic influenza A/H1N1 than with seasonal influenza.
  
  
  METHODS
  From September 1, 2009, to January 31, 2010, a specialized clinic for patients (aged ≥15 years) with ILI was operated in Korea University Guro Hospital. RT-PCR assay was performed to diagnose 2009 pandemic influenza A/H1N1. A retrospective case-case-control study was performed to determine the predictive factors for influenza pneumonia and to discriminate concomitant/secondary bacterial pneumonia from primary influenza pneumonia during the 2009-2010 pandemic.
  
  
  RESULTS
  During the study period, the proportions of fatal cases and pneumonia development were 0·12% and 1·59%, respectively. Patients with pneumonic influenza were less likely to have nasal symptoms and extra-pulmonary symptoms (myalgia, headache, and diarrhea) compared to patients with non-pneumonic influenza. Crackle was audible in just about half of the patients with pneumonic influenza (38·5% of patients with primary influenza pneumonia and 53·3% of patients with concomitant/secondary bacterial pneumonia). Procalcitonin, C-reactive protein (CRP), and lactate dehydrogenase were markedly increased in patients with influenza pneumonia. Furthermore, procalcitonin (cutoff value 0·35 ng/ml, sensitivity 81·8%, and specificity 66·7%) and CRP (cutoff value 86·5 mg/IU, sensitivity 81·8%, and specificity 59·3%) were discriminative between patients with concomitant/secondary bacterial pneumonia and patients with primary influenza pneumonia.
  
  
  CONCLUSIONS
  Considering the subtle manifestations of 2009 pandemic influenza A/H1N1 pneumonia in the early stage, high clinical suspicion is required to detect this condition. Both procalcitonin and CRP would be helpful to differentiate primary influenza pneumonia from concomitant/secondary bacterial pneumonia.
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Korea University College of Medicine, Seoul, Korea.
authors.forename: Joon Y
authors.initials: JY
authors.lastname: Song
authors.forename: Hee J
authors.initials: HJ
authors.lastname: Cheong
authors.forename: Jung Y
authors.initials: JY
authors.lastname: Heo
authors.forename: Ji Y
authors.initials: JY
authors.lastname: Noh
authors.forename: Hwan S
authors.initials: HS
authors.lastname: Yong
authors.forename: Yoon K
authors.initials: YK
authors.lastname: Kim
authors.forename: Eun Y
authors.initials: EY
authors.lastname: Kang
authors.forename: Won S
authors.initials: WS
authors.lastname: Choi
authors.forename: Yu M
authors.initials: YM
authors.lastname: Jo
authors.forename: Woo J
authors.initials: WJ
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002097:C-Reactive Protein / Q000032:analysis; D002116:Calcitonin / Q000097:blood; D015740:Calcitonin Gene-Related Peptide; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D007251:Influenza, Human / Q000150:complications / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000821:virology; D007723:Korea; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D018410:Pneumonia, Bacterial / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000209:etiology; D011024:Pneumonia, Viral / Q000150:complications / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000821:virology; D011498:Protein Precursors / Q000097:blood; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: C000606589:CALCA protein, human; D011498:Protein Precursors; D002116:Calcitonin; D002097:C-Reactive Protein; D015740:Calcitonin Gene-Related Peptide