Performance of a Rapid Diagnostic Test for Influenza in a Tertiary Military Hospital, Philippines

Introduction: It is important to evaluate the performance of existing rapid influenza diagnostic tests (RIDTs) and the factors that can affect performance especially when the circulation dynamics of influenza strains change such as the displacement and replacement of the circulating seasonal influenza strains. Materials and Methods: Nasal swabs were collected from patients presenting at V Luna Medical Center, Armed Forces of the Philippines Health Service Command, with influenza-like illness (ILI) with one swab tested using Quickvue (QV) influenza A+B RIDT (Quidel) and the other swab tested using the ABI 7500 (Applied Biosystems) real-time reverse transcriptase-polymerase chain reaction. Sensitivity, specificity, positive predictive value, and negative predictive value were estimated. We identified clinical symptoms predictive of influenza subtype and evaluated the independence of QV sensitivity on (1) Cycle threshold (Ct) value, controlling for timing of collection; (2) timing of collection, controlling for Ct value; and (3) Ct value and timing of collection taken together. Results: Between August 2011 and October 2016, patients presenting with ILI (n = 2333) underwent testing. Quickvue sensitivity across all subtypes was significantly correlated with lower Ct values (higher virus titers) (P <.001) and, except for flu A/H3 (P=.974), was also significantly associated with timing of specimen collection (P <.05). No statistically significant difference was noted in QV sensitivity for Flu A/H3 (P=.130), pandemic H1/N1 (P=.207), Flu A/H3+ pandemic H1/N1 (P=.341), and Flu B (P=.103) across different age groups but sensitivity of QV significantly differed (P < .001) across the different influenza subtypes. Conclusion: Overall specificity of QV was high across all flu subtypes, but overall sensitivity was low (Flu A/pdm H1) to moderate (Flu A/H3 and Flu B). The findings highlight the need to develop more sensitive influenza RDTs to detect circulating influenza strains and the use of the quadrivalent flu vaccine during the annual influenza vaccination.