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Background In early April 2009,cases of human infection with 2009 pandemic influenza A (H1N 1) virus were identified in Mexico.The virus then spread rapidly to other regions of the world.From October 2009,sporadic imported cases of novel influenza A (H1N1) were continuously confirmed in Suzhou.The aim of the study was to review the chest CT findings in 63 patients with laboratory-confirmed novel swine-origin influenza A (H1N1) virus (S-OIV) infection.Methods Chest CT examinations were collected from 63 S-OIV infected patients during their hospital stay.Three experienced radiologists inspected images to qualitatively and quantitatively characterize S-OIV induced image changes.CT scores of lesion severity were calculated based on the percentage of affected area to determine severity of infectious lesions.Patients were divided into two groups based on the leukocyte counts.Lesion patterns,local distributions,and quantitative measures were investigated and compared between the two groups.Results Various degrees of bilateral multifocal lesions of ground-glass opacities were found with or without consolidations on the chest CT images.The lesions were both bronchocentric and centrilobular.Patients with elevated leukocyte counts had more extensive lesions,in terms of severity and affected area,than the patients with normal leukocyte counts.The lesion severity scores of patients in the elevated leukocyte group were significantly higher than those of the normal leukocyte group in terms of the entire lung area (P ＜0.01),and upper (P ＜0.05) and lower (P ＜0.01)lobes as well.There were changes in the CT characteristics seen at follow-up as demonstrated by lesions absorption (P＜0.01),especially in the upper lobe of the lung (P ＜0.01),but less so in the middle lobe/lingual and lower lobe of the lung (P＞0.05).Conclusions The most common CT findings in S-OIV infection patients were bilateral multifocal distributed ground-glass opacities and consolidations.The lesions were located dominantly at bronchocentric and centrilobular areas.Lung lesions were more obviously absorbed in upper lobes between two examinations.The observations and analysis from this study provide information that may be useful in image understanding and patient management for future pandemic influenza.