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.