Unlike S.pneumoniae, S.aureus and S.pyogenes which are repeatedly reported as coinfecting agents [4, 8, 10, 13] , the high rates of M.pneumoniae coinfection was unique to our study. Although hematological parameters have been mentioned in few other studies [8, 9, 12] , to our best knowledge this is the first study that specifically explored the impact of bacterial coinfection on these parameters. CDC recognizes the importance of early empirical antibiotics in H1N1 infected patients who might have concurrent bacterial pneumonia [13] . Our study showed that leukocytosis and neutrophilia were notably higher in bacterial coinfected patients. This finding could alert physicians about the possibility of bacterial coinfection, as clinical diagnosis may be insufficient and bacterial cultures take time. Eighty-two percent of our patients received empiric or definitive antibiotics at some point during admission which was comparable to high rates in a China study [9] .