uHigh Sensitivity of a Rapid Immunochromatographic Test for the Detection of Influenza A Virus 2009 H1N1 on Nasopharyngeal Aspirates from Young Children

Recent reports have suggested that immunochomatographic tests (ICT’s) have poor sensitivity for Influenza A Virus 2009 H1N1 (H1N1 09) infection on swabs2 and nasopharyngeal washes1, but they do have advantages including short turnaround time, lack of hardware, and minimal validation requirements6. We used the QuickVue Influenza A+B ICT test (Quidel Corp, San Diego, CA) during the 2009 Australian winter at a major pediatric teaching hospital. Here we provide in-use pediatric ICT performance estimates for H1N1 09, examine the effect of age and specimen type on sensitivity, and discuss the utility of ICT assays in guiding treatment and infection control decisions.

Once H1N1 began circulating, our state public health response had two phases: In the “contain phase” (22nd May to 16th June 2009) all patients presenting with influenza-like illness were tested. A specimen aliquot was sent to the state reference laboratory for Influenza A testing and strain typing by PCR2.. These results took over 48 hours which was too slow for therapeutic or infection control purposes. During the “protect phase” (17th June onwards), only admitted patients and those with underlying medical conditions had specimens collected, and only specimens positive for Influenza A by local testing were referred for PCR confirmation. Nasopharyngeal aspiration (NPA) was performed with a 6- or 8-French flexible suction catheter with attached sputum trap. Flocked nasal swabs with universal transport medium (UTM® Kit, Copan, CA) and a rayon throat swab were combined for processing.

Our laboratory performed the ICT according to the manufacturer’s instructions. Direct fluorescent antibody (DFA) testing for respiratory viruses using the Similfluor Respiratory Screen (Chemicon, CA) was performed on all specimens negative or not tested by the ICT. This assay detects Influenza Virus A&B, Respiratory Syncytial Virus, Parainfluenza Virus 1,2 &3, Adenovirus, and Human Metapneumovirus. All specimens negative by DFA were cultured on R-Mix cells (Diagnostic Hybrids, Ohio) for 3 days then stained with Influenza A antibodies (Imagen, DaktoCytomation, Ely, UK). All specimens positive for Influenza A by any local test (ICT, DFA or culture) were referred for confirmatory Influenza A PCR and strain typing.