Background: Rapid and accurate diagnosis is essential for containing the novel influenza A/H1N1 pandemic. Polymerase chain reaction (PCR) testing is an accurate diagnostic method, but it is not routinely available worldwide. We herein evaluated the usefulness of pharyngeal “influenza follicles” in diagnosing seasonal influenza and influenza A/2009 (H1N1) pdm.
Methods: Between August 3 and October 29, 2009, we evaluated 87 patients with influenza-like symptoms. Twenty-three had influenza follicles (22 on initial evaluation; 1 on follow-up) while 64 did not. Considering these two groups, we then compared the positive cases using rapid diagnostic testing (confirmed by PCR). In addition, 419 cases of seasonal influenza diagnosed between 2003 and 2009 were examined for the presence of influenza follicles based on Miyamoto's 2007 definition⁹, and new exclusion criteria were developed.
Results: Among the 23 patients with influenza follicles, 21 were diagnosed with novel influenza. Of these, follicles were present on initial evaluation in 20 and on follow-up in 1. None of the 64 patients without influenza follicles were diagnosed with influenza (sensitivity 100%, specificity 97%). Among the 419 patients diagnosed with seasonal influenza between 2003 and 2009, influenza follicles occurred in all type A/H3N2, A/H1N1, and B cases (sensitivity 95.46%, specificity 98.42%). Thus, follicles were considered a specific sign of influenza.
Conclusion: Influenza follicles occur in both seasonal and novel influenza. This identification method has higher diagnostic sensitivity and specificity than rapid diagnostic testing and is a promising clinical tool for diagnosing influenza when PCR is unavailable, or in pandemic situations.