RAPID DIAGNOSTIC TESTING FOR INFLUENZA: AN EVIDENCE-BASED REVIEW AND COMPARISON WITH UNAIDED CLINICAL DIAGNOSIS

Background: Worldwide, influenza imposes considerable health and economic burden. Clinical diagnosis of influenza-like illness (ILI) is complicated by non-specific symptomatology. The use of rapid flu tests (RFTs) impact treatment decisions and may improve patient care, but guidelines for RFT use are non-specific. Moreover, the relative performance of unaided clinical diagnosis compared to RFTs is unclear. Purpose: To systematically review: 1) the comparative performance of RFTs and unaided clinical diagnosis of influenza; 2) the impact of RFTs on outcomes of clinical decision-making; and 3) the factors associated with poorer clinical diagnostic discrimination in patients with ILI. Methods: A systematic literature review was based on defined article selection criteria identifying published research across various clinical settings. The searched databases included: PubMed/MEDLINE, the Cochrane Library, and other pertinent sources of articles reporting sensitivity, specificity, and effects of RFT and clinical diagnosis on decision-making regarding the management of patients with ILI. Age-stratified, weighted-average sensitivities & specificities of the widely-used RFT, QuickVue®, were calculated and factors associated with poorer clinical diagnostic discrimination were sought. Results: QuickVue’s® diagnostic specificity generally exceeds that of unaided clinical diagnosis by approximately 28%. False positive results are estimated to occur 6.4 times more frequently by unaided clinical diagnosis than by use of the RFT alone. These findings are unaffected by disease prevalence (i.e. seasonality). RFT use reduces diagnostic testing, antibiotic use, and emergency department length of stay, while increasing antiviral prescription rates. The most consistent factor associated with average-to-low unaided clinical diagnostic specificity for influenza was the clinical presentation of “fever and cough” being used as the primary diagnostic criterion. Conclusions: QuickVue’s® performance as a diagnostic test exceeds that of unaided clinical diagnosis. RFTs affect the outcomes of informed clinical decision-making. Broader clinical diagnostic criteria for ILI, combined with RFT use, will most likely improve overall diagnostic specificity.  Taken together, these results provide an improved framework upon which to diagnose influenza, design future comparative RFT studies, and develop specific guidelines for improved ILI patient management.