Background: Rapid and accurate diagnosis is essential for containing an influenza pandemic. Rapid diagnostic tests are routinely available but sometimes give false-negative results, especially during the early phase of influenza infection. The usefulness of the presence of pharyngeal “influenza follicles” on physical examination for the diagnosis of influenza A/ H1N12009 was evaluated. Methods: Between August 16, 2009 and January 31, 2010, 453 patients with influenza-like symptoms were evaluated, of whom 110 were diagnosed as having type A influenza (99.33% were diagnosed as having influenza A/H1N1 2009 in Ibaraki Prefecture). We previously reported 23 patients that had been diagnosed as having influenza between August 16 and October 29, 2009 (first period).
4) Between November 2, 2009 and January 31, 2010 (second period), 87 of 348 patients with influenza-like symptoms were diagnosed as having influenza and were subsequently evaluated. Results: Of the 87 patients diagnosed as having influenza, 86 were found to have influenza follicles during the initial evaluation. Rapid diagnostic testing was positive in 77 patients upon initial examination, 8 became positive on the second day, and 2 became positive on the third day. Even though no influenza follicles were found in 1 of the patients that had been diagnosed as having influenza, no follicles were found in any of the 261 patients that were diagnosed as not having influenza. The sensitivity of diagnosing influenza with influenza follicles was 87/88 = 98.8%, the specificity was 261/0 + 261=100%, the positive predictive value was 86/86 + 0 = 100%, the negative predictive value was 1/1 + 261 = 0.37%, LR + was (86/[86 +1] / (0/[0 + 261]) = ∞, and LR- was (1/[86 +1]) / (261/[0 + 261]) = 1.1%. Interobserver reliability was demonstrated by κ = 0.557 (p < 0.001). Conclusion: Determining the presence of “influenza follicles” provides higher sensitivity and specificity than rapid diagnostic tests and is promising as a clinical tool for worldwide use in a pandemic situation. Considering modern advances in technology, both the meaning and value of the physical examination require re-evaluation.
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