It is reported that patients with 2009 H1N1 virus infections had a relative leukopenia with lymphopenia [18, 19] . However addition to this finding, we found in the present study that the patients with pneumonia had a higher WBC count with lower lymphocyte differential, and the more severely affected patients had the highest WBC with the lowest lymphocyte differential in the early stages of the infection (within two days of fever onset). Previous human studies of H5N1 virus infections have revealed that a lower lymphocyte count was associated with a poor outcome [20] , and mice infected with influenza viruses showed a lymphopenia and the H5N1 subtype was associated with marked lymphopenia with total lymphoid depletion [21] . Therefore peripheral lymphocyte may be associated with the pathogenesis of acute lung injury in influenza virus infections [9] . Altered CRP and ESR values were not prominent in 2009 H1N1 virus infections, but higher CRP values were associated with a more severe illness.