Diagnostic performances of the Xpert® Flu PCR test and the OSOM® immunochromatographic rapid test for influenza A and B virus among adult patients in the Emergency Department.

BACKGROUND:New rapid influenza diagnostic tests (RIDT) are available but their clinical utility in adults has not been validated. OBJECTIVES:To evaluate the diagnostic performances of OSOM® Ultra Flu A&B a RIDT on viral strains of influenza A/B from the last epidemic season, and its feasibility by Emergency Department (ED) physicians and nurses. STUDY DESIGN:Of the 1099 patients admitted to the ED with suspected influenza, all having a nasopharyngeal swab tested by the Xpert® Flu PCR and then stored at -20 °C; 500 were selected at random and their samples were tested using the RIDT. Two experts reviewed ED and hospital medical records and all virological data to define influenza cases. Intra- and inter-observer variability were calculated. RESULTS:Of the 500 patients included 45% were ≥75 years, 122 (24.4%) presented with influenza based on clinical and virological criteria. PCR test performances (%) were Se 98.4 (95% CI 93.6-99.7), Spe 99.7 (98.3-100), PPV 99.2 (94.8-100) and NPV 99.5 (97.9-100); and RIDT performances were Se 95.1 (89.2-97.9), Spe 98.4 (96.4-99.4), PPV 95.1 (87.2-99.9) and NPV 98.4 (96.4-98). There was no difference in test performance between influenza A and B virus nor between the influenza A subtypes. Intra- and inter-observer variability of RIDT were 0.94 (0.89-0.99) and 0.96 (0.92-1). CONCLUSION:Our results show that the Xpert® Flu PCR and the OSOM® Ultra Flu A&B Test perform very well in diagnosing strains of circulating virus in adults and elderly. Our results also confirm the feasibility of this RIDT at point-of-care by ED staff.