Clinical and Radiographic Comparison of Influenza Virus-associated Pneumonia among Three Viral Subtypes

Objective Presently, the predominant subtypes of influenza viruses in the world, except for those in local epidemics, include influenza pandemic H1N1 2009 (pH1N1), H3N2, and B viruses. There are few reports on the differences in the clinical features, radiographic findings, treatment, and outcomes of influenza virus-associated pneumonia among these three viral subtypes. The purpose of this study was to investigate whether the clinical features, radiographic findings, treatment, and outcomes differ among the viral subtypes. Methods We retrospectively analyzed 96 patients with influenza virus-associated pneumonia whose viral subtypes were clarified. Results Patients with pH1N1 virus-associated pneumonia tended to be young. The frequency of primary viral pneumonia differed among the virus-associated pneumonia subtypes (pH1N1, 80%; H3N2, 26.5%; and B, 31%). Patients with pH1N1 virus-associated pneumonia more frequently showed bilateral ground-glass opacities (GGOs), which affected more lobes than in patients with H3N2 and B virus-associated pneumonia. However, patients with H3N2 virus-associated pneumonia showed a higher frequency of consolidation and diffuse bronchial wall thickening than did the patients with pH1N1 virus-associated pneumonia. The severity and mortality did not differ among the three pneumonia subtypes. Conclusion In the patients who developed influenza virus-associated pneumonia, those with pH1N1 virus-associated pneumonia frequently developed primary viral pneumonia resulting in bilateral and broad areas of GGOs on imaging, whereas patients with H3N2 virus-associated pneumonia frequently showed consolidation and diffuse bronchial wall thickening on pulmonary imaging.