title: Symptomatic predictors for 2009 influenza A virus (H1N1) infection with an emphasis for patients with a negative rapid diagnostic test.
abstract: BACKGROUND
  The clinical diagnosis of influenza is difficult because it shares nonspecific symptoms with a variety of diseases. Emergency departments and clinics were overwhelmed by a surge of anxious patients during the 2009 influenza A virus (H1N1) outbreak. Our objective was to identify symptomatic predictors of influenza virus infection for patients with a negative rapid diagnostic test.
  
  
  RESULTS
  We conducted a retrospective review of 805 patients who presented at Chang Gung Memorial Hospital, from August 1, 2009, to September 30, 2009. Respiratory specimens from these patients were subjected to rapid influenza tests and reverse-transcription polymerase chain reactions. In total, 36% of 308 children and 23% of 497 adults were positive for 2009 influenza A virus (H1N1) infection by polymerase chain reaction or virus culture. For pediatric patients, sore throat and influenza-like illness significantly increased the odds of having 2009 influenza A virus (H1N1) infection, by more than 3-fold (95% confidence interval (CI): 1.9-7.3) and 7-fold (95% CI: 4.00-14.2), respectively. For adult patients, cough and constitutional symptoms increased the odds of having 2009 influenza A virus (H1N1) by greater than 5-fold (95% CI: 3.1-10.2) and 3-fold (95% CI: 2.1-6.7), respectively. The negative likelihood ratio of the combination of fever and cough was 0.096 (95% CI: 0.01-0.69) for children with negative results of rapid influenza diagnostic tests.
  
  
  CONCLUSIONS
  In influenza epidemic settings, clinicians should be aware that rapid influenza diagnostic tests are relatively insensitive for the diagnosis of influenza virus infection. For patients with negative rapid influenza diagnostic tests, those lacking fever and cough have a low probability of influenza virus infection. The management strategy should be made individually and depend on the severity of illness.
authors.affiliation: Department of Pediatrics, Chang Gung Memorial Hospital, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Chen-Yen
authors.initials: CY
authors.lastname: Kuo
authors.forename: Yhu-Chering
authors.initials: YC
authors.lastname: Huang
authors.forename: Chung-Guei
authors.initials: CG
authors.lastname: Huang
authors.forename: Kuo-Chien
authors.initials: KC
authors.lastname: Tsao
authors.forename: Tzou-Yien
authors.initials: TY
authors.lastname: Lin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003140:Communicable Disease Control / Q000379:methods; D003955:Diagnostic Tests, Routine; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000378:metabolism*; D007251:Influenza, Human / Q000175:diagnosis* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013624:Taiwan