Abstract： Objective This study's objective was to analyze the clinical characteristics of the 2009 influenza A (H1N1) virus,as well as how its clinical characteristics relate to patient gender.Methods A total of 224 2009 influenza A (H1N1) patients cured and discharged by the clinical center for public health of Shanghai between May 24 and July 20,2009 were included in the study.The patients' personal information,signs and symptoms,lab and imagery data,disease course,hospitalization period and negative seroconversion duration of nucleic acid after antiviral treatment were analyzed.Results Among the 224 paand 40 years old.Clinical manifestations included fever,cough and congestion of the throat,and lab findings were characterized by elevated C-reaction protein (CRP) and neutrophil,and the levels of white blood cell (WBC) and CRP were significantly increased in male patients compared to female patients[ (6.71 ±2.45) × 109/L vs (5.74±2.10) × 109/L,F =10.063,P =0.002;(16.32 ±18.27)mg/L vs (12.05±11.44) mg/L,F = 4.026,P = 0.046,respectively ].Female patients had significantly lower serum prealbumin (PA) levels than male patients [ (244.80 ± 76.05) mg/L vs (272.06 ± 93.51) mg/L,F = 5.800,P = 0.017 ].The patients' serum CRF levels significantly decreased after the treatment [ (3.81 ± 4.93)mg/L vs (10.80 ± 12.92) mg/L,F = 6.709,P =0.013 ],while the levels of CD3,CD4 and CD8 significantly increased after treatment [ (1449.46 ± 446.71) cell/μl vs (700.50 ± 307.46) cell/μl,F =57.940,P =0.000;(762.69 ±255.66) cell/μl vs (370.08 ± 157.62) cell/μl,F =47.587,P =0.000;(592.38 ±238.24) cell/μl vs (288.88 ± 164.98) cell/μl,F =34.409,P =0.000,respectively].Approximately 29.9% of the patients had abnormal signs on chest CT imagery,and 21.9% had obvious signs indicating pneumonia.The average disease course was (3.9± 1.4) days,the negative seroconversion duration of the mRNA after antiviral treatment was (3.8 ± 1.3) days,and the average hospitalization period was (5.0 ± 1.7) days.Conclusion The most significant lab findings of 2009 influenza A (H1N1) virus was characterized by fever,cough and throat congestion with elevated CRP and neutrophil.The 2009 influenza A (H1N1) strain was able to affect multiple organs,including hepatic synthesis of PA as well as immune functioning.The 2009 influenza A (H1N1) influenza virus strain was clinically mild,with short disease course and good prognosis.