Near-patient assays for diagnosis of influenza virus infection in adult patients

Rapid and reliable diagnosis of influenza is essential for identification of contagious patients and effective patient management. Near-patient assays allow establishment of the diagnosis within minutes in young children, and this study aimed to evaluate near-patient assays in relation to the patient's age. A total of 194 patients with laboratory-confirmed influenza A/H3N2 virus infection, diagnosed within a prospective cohort study, were included. Cryopreserved nasopharyngeal swabs collected from these patients were tested by four near-patient assays (Binax Now Influenza A&B, Quick S-Influ A/B, Influ-A&B Respi-Strip, and Actim Influenza A&B). The main outcome measure was sensitivity of the near-patient assays in relation to the age of patients. The Binax Now, Quick S-Influ, Influ-A&B Respi-Strip and Actim assays had overall sensitivities of 19%, 18%, 26%, and 40%, respectively. The estimated sensitivity for influenza A/H3N2 virus detection in nasopharyngeal swabs was 17-56% in children 1 year of age and decreased to 8-22% in patients 80 years of age (logistic regression). The sensitivity of the Influ-A&B Respi-Strip and Actim assays decreased significantly with increasing age (p 0.014 and p 0.033, respectively (logistic regression)), a trend for decrease was observed for the Binax Now assay (p 0.074 (logistic regression)), and the low sensitivity of the Quick S-Influ assay was similar in children and adults. Less than one-fourth of diagnosed influenza A/H3N2 virus infections can be identified in elderly patients using a near-patient assay. Consequently, near-patient assays are of limited value for confirming the diagnosis when influenza is clinically suspected in adults. Antiviral therapy and additional diagnostic procedures cannot be withheld on the basis of a negative near-patient assay result, particularly in adult patients.