title: Comparison of the Directigen flu A+B test, the QuickVue influenza test, and clinical case definition to viral culture and reverse transcription-PCR for rapid diagnosis of influenza virus infection.
abstract: The diagnostic performances of the clinical case definition of influenza virus infection based on the combination of fever and cough and of two rapid influenza diagnostic tests, the Directigen Flu A+B test (Directigen; BD Diagnostic Systems, Sparks, Md.) and the QuickVue influenza test (QuickVue; Quidel, San Diego, Calif.), were compared to those of viral culture and an in-house reverse transcription (RT)-PCR during the 2000-2001 flu season. Two hundred consecutive nasopharyngeal aspirates were analyzed from 192 patients, including 122 adults and 70 children. Viral culture identified influenza virus A in 16 samples and influenza virus B in 55 samples, whereas RT-PCR identified influenza virus A in 21 samples and influenza virus B in 64 samples. When RT-PCR was used as the reference standard, the likelihood ratios for a positive test were 40.0 for Directigen, 8.6 for QuickVue, and 1.4 for the combination of fever and cough, whereas the likelihood ratios for a negative test were 0.22, 0.16, and 0.48, respectively. Our study suggests that (i). the poor specificity (35 to 58%) and the poor positive predictive value (41 to 60%) of the clinical case definition of influenza preclude its use for prediction of influenza virus infections during epidemics, especially when infection control decision making in the hospital setting is considered; (ii). Directigen has a higher diagnostic yield than QuickVue but is associated with a larger number of invalid results; (iii). the sensitivities of the rapid diagnostic tests are significantly lower with samples from adults than with samples from children, with the rates of false-negative results reaching up to 29%; and (iv). RT-PCR detects more cases of influenza than viral culture, and this greater accuracy makes it a more useful reference standard.
authors.affiliation: Department of Microbiology and Infectious Diseases, Faculté de Médecine de l'Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Annie
authors.initials: A
authors.lastname: Ruest
authors.forename: Sophie
authors.initials: S
authors.lastname: Michaud
authors.forename: Sylvie
authors.initials: S
authors.lastname: Deslandes
authors.forename: Eric H
authors.initials: EH
authors.lastname: Frost
mesh_terms: D001483:Base Sequence; D019411:Clinical Laboratory Techniques; D017931:DNA Primers; D006801:Humans; D009980:Influenza A virus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D009981:Influenza B virus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D016133:Polymerase Chain Reaction / Q000379:methods; D012367:RNA, Viral / Q000235:genetics / Q000302:isolation & purification*; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity
chemical_list: D017931:DNA Primers; D012367:RNA, Viral