title: [Predictive factors of 2009 H1N1 virus infection in patients with influenza syndrome].
abstract: BACKGROUND
  Polymerase chain reaction (PCR) testing is one of the better techniques for viral detection in nasopharyngeal swabs. The objective of this study was to assess the percentage of positive swabs and to determine whether there were differences according to PCR positivity.
  
  
  METHODS
  A retrospective study of 362 patients with flu syndrome attended at the Emergency Department between July 15 and December 15, 2009, in whom PCR of nasopharyngeal swabs for the detection of H1N1 2009 influenza virus was performed. Those cases in which swab testing was adequately requested were identified, and patients were divided into two groups according to positive or negative results for H1N1 2009 influenza virus.
  
  
  RESULTS
  Nasopharyngeal swab was inadequately ordered in 87. In the remaining 275 patients, PCR was positive in 141. Patients with positive nasopharyngeal swabs were younger (mean [SD] age 36.1 [15] vs 42.3 [18] years, P= 0.002), had lower white blood cell, neutrophil and lymphocyte counts, lower serum concentrations of C-reactive protein (5.15 [5] vs 10.5[12] mg/dL, P= 0.036) and lower incidence of radiological infiltrates (20.5% vs 33%, P= 0.036). In the logistic regression analysis, age, serum C-reactive protein levels, and lymphocyte count were independently associated with a positive nasopharyngeal swab.
  
  
  CONCLUSIONS
  About 50% of patients with flu syndrome had positive nasopharyngeal swabs for H1N1 2009 influenza virus. Age, C-reactive protein, and lymphocyte count were independent predictors of positivity.
authors.affiliation: Servicio de Urgencias, Hospital Universitario del Mar, Barcelona, Spain. asupervia@hospitaldelmar.cat
authors.forename: A
authors.initials: A
authors.lastname: Supervía
authors.forename: F
authors.initials: F
authors.lastname: Del Baño
authors.forename: G
authors.initials: G
authors.lastname: Maldonado
authors.forename: O
authors.initials: O
authors.lastname: Pallàs
authors.forename: A
authors.initials: A
authors.lastname: Aguirre
authors.forename: C
authors.initials: C
authors.lastname: Vilaplana
authors.forename: J P
authors.initials: JP
authors.lastname: Horcajada
authors.forename: M T
authors.initials: MT
authors.lastname: Martínez-Izquierdo
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D002097:C-Reactive Protein / Q000032:analysis; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000175:diagnosis* / Q000821:virology; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D009305:Nasopharynx / Q000821:virology; D011237:Predictive Value of Tests; D012372:ROC Curve; D012044:Regression Analysis; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012307:Risk Factors; D013030:Spain
chemical_list: D002097:C-Reactive Protein