While airspace disease was observed more often in patients with non-influenza viruses, there were no chest radiographic findings that distinguish influenza infection. Over half of patients with pH1N1 had non-specific findings on chest radiograph as previously reported . Our study supports previous findings that pH1N1 tends to infect younger SB203580 p38 MAPK inhibitor adults, sparing the elderly and young children . We found lower rates of influenza from nursing home patients reflecting this age distribution. Of those that died or were hospitalized, many had co-morbidities as previously reported . In contrast to other studies , we did not find a high infection or mortality rate during pregnancy but our study was underpowered due to the low number of pregnant women in our cohort. The mortality rate of 2.1% for hospitalized patients with pH1N1 infection in our cohort was lower than other reports . Despite this, it was significantly higher than the mortality associated with other respiratory viral infections and highlights the importance of accurate diagnosis and early treatment of influenza infection. Aside from the retrospective nature of our study, a potential limitation was the small number of pregnant women likely due to the presence of a neighboring obstetrics and gynecologic hospital. A second limitation was the time period for which patients presenting with ILI were evaluated whereas a typical respiratory season would be for several months and include a greater variety of viruses, especially in the pediatric population. In fact, our data does indicate that after the pandemic wave at our institution, a typical peak for RSV, metapneumovirus and parainfluenza viruses followed the presence of pH1N1, much like the rest of the country. A third limitation was that pH1N1 confirmatory testing was not performed for all nonsubtypeable influenza A viruses. However, recent literature suggests that 100% of non-subtypeable influenza A H1 identified by the xTAG RVP was pH1N1 and that misinterpretation is uncommon . In addition, our initial investigation of a large number of strains early in the pandemic with the CDC PCR assay confirmed these findings.