994 Differences in the Epidemiology and Clinical Outcomes of Pandemic (H1N1) 2009 Influenza vs. Seasonal Influenza

Sunday, March 21, 2010
Grand Hall (Hyatt Regency Atlanta)
Kevin T. Shiley, MD , University of Pennsylvania, Philadelphia, PA
Neil Fishman , University of Pennsylvania School of Medicine, Philadelphia, PA
Ebbing Lautenbach, MD, MPH, MSCE , University of Pennsylvania School of Medicine, Philadelphia, PA

There are limited data comparing the clinical presentations, comorbidities, and outcomes of patients with infections due to seasonal influenza with Pandemic (H1N1) 2009 influenza. 


To compare the epidemiology and clinical characteristics of Pandemic (H1N1) 2009 influenza with seasonal influenza.


A cross-sectional study was conducted to compare the epidemiology and outcomes of infections due to seasonal influenza with infections from Pandemic (H1N1) 2009 influenza among patients seen in the emergency department or hospital setting.  Subjects were enrolled at two affiliated academic medical centers in Philadelphia.  Cases of seasonal influenza were identified from the 2005-2006 and 2007-2008 influenza seasons while Pandemic (H1N1) 2009 cases were enrolled from May 1, 2009 to August 7, 2009.


Forty-nine cases of Pandemic (H1N1) 2009 and 503 cases of seasonal influenza were identified during the study periods. Lower age and African American race were found more often in Pandemic (H1N1) 2009 cases.  Several symptoms were more common among patients with Pandemic (H1N1) 2009 compared to seasonal influenza infections: cough (98% vs. 83%; p=0.007), myalgias (71% vs. 46%; p=0.001) and pleuritic chest pain (45% vs. 15%; p<0.001).   Pregnancy was the only comorbidity that occurred significantly more often in the Pandemic (H1N1) 2009 group (16% vs. 1%; p<0.001). There were no significant differences in frequencies of inhospital death, intensive care unit admission, or length of hospitalization between groups.


Other than pregnancy, there were few clinically significant differences between infections from seasonal and Pandemic (H1N1) 2009 influenza.   The greater rates of lower respiratory tract symptoms in Pandemic (H1N1) 2009 cases might serve to differentiate it from seasonal influenza. The similarity in outcomes between groups suggests that Pandemic (H1N1) 2009 does not confer worse clinical outcomes than seasonal influenza.