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.