LAUSR

Abstract Background Lymphopenia has been observed in severe pandemic influenza A/H1N1 in developed countries. However, data from developing countries are rare and dynamic change of lymphocyte counts in severe pandemic influenza A/H1N1 is scarcely reported. This study aimed to observe change of lymphocyte counts in patients with severe pandemic influenza A/H1N1 and to investigate the correlation of lymphopenia and severe pandemic influenza A/H1N1. Methods We retrospectively analyzed the white blood cell counts and differentials and other clinical data in 21 hospitalized patients with severe pandemic influenza A/H1N1 confirmed by reverse-transcription PCR during 2009 and 2010. Results All patients, except two cases with bacterial co-infections, had normal or reduced white blood cell counts. Seventeen (81.0%) patients had decreased lymphocyte proportions (<20%) and counts (<0.8×109/L), with the lowest value of 1.2% and 0.1×109/L respectively. A patient with nosocomial infection of influenza A/H1N1 showed that lymphopenia occurred on the first day of illness. Lymphocyte proportions and absolute counts returned to normal or slightly higher than normal in 16 of the 17 patients within 2–3weeks after the disease onset. Conclusions Lymphopenia along with other clinical parameters may be helpful in early differential diagnosis of severe pandemic influenza A/H1N1.