Chest Infections |

Catching the Flu: Clinical Implications of Two Different Molecular Testing Methods Used During the 2013-2014 Influenza Season FREE TO VIEW

Nicholas Csikesz, MD; Sonja Chen, MD; Jacob Smith, MD; Roberta Dickenson; Kimberle Chapin; Gerardo Carino, MD
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Brown University, Providence, RI

Chest. 2015;148(4_MeetingAbstracts):117A. doi:10.1378/chest.2266627
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SESSION TITLE: Chest Infections Posters I

SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 28, 2015 at 01:30 PM - 02:30 PM

PURPOSE: Influenza-like illness is common but not always due to influenza virus. Diagnostic testing to identify true influenza cases has important clinical implications. Molecular testing methods are now commonly used for this purpose, including multiplex RT-PCR to test for multiple respiratory viruses (RVP) and single analyte realtime PCR (rPCR) for influenza specifically. In our institutions, the specific assays used are the xTAG® Respiratory Viral Panel (RVP) and Cepheid Xpert® Flu (rPCR). Published literature on the Xpert Flu test suggests that it is highly sensitive, however several cases in which an initial negative rPCR test was followed by an RVP test that was positive for influenza suggested that this may not be the case. This investigation assesses the performance of the Xpert Flu test in patients with RVP-confirmed influenza and identifies subsequent clinical ramifications.

METHODS: A retrospective chart review was performed of all patients who had an rPCR performed within 7 days before or after a positive RVP for influenza. The performance of the rPCR was then assessed. Clinical information obtained included demographics, patient comorbidities, patient vaccination status, testing characteristics, and selected outcome measures.

RESULTS: In the 2013-2014 influenza season, there were 176 patients who tested positive for influenza by RVP and had an rPCR test done within a 7 day period. This included 130 patients with influenza A and 46 patients with influenza B. The rPCR test was positive for influenza in only 56% of these cases (58% of influenza A, 52% of influenza B). The rPCR was less likely to be positive when testing was not performed on the same date (p<0.01). No other patient or test factors were identified that increased the likelihood of a false negative result. Patients with false negative rPCR tests were less likely to be treated with oseltamivir (p<0.01).

CONCLUSIONS: In patients with RVP-proven influenza who had concomitant testing with the Xpert Flu PCR test during the 2013-2014 influenza season, the Xpert Flu test failed to detect a significant number of cases of influenza. The patients who had a false negative Xpert Flu test were less likely to receive treatment with oseltamivir.

CLINICAL IMPLICATIONS: Caution should be advised for clinicians treating patients with suspected influenza. Confirmatory testing with a respiratory viral panel may be appropriate in admitted or severely ill patients when a primary flu test is negative.

DISCLOSURE: The following authors have nothing to disclose: Nicholas Csikesz, Sonja Chen, Jacob Smith, Roberta Dickenson, Kimberle Chapin, Gerardo Carino

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