Differences in sentinel influenza confirmed incidence rates and clinical presentation of influenza virus 2008-09 seasonal vs. 2009-10 pandemic influenza

The Influenza sentinel surveillance network of Catalonia (PIDIRAC) allows for the study of circulating influenza virus (IV). The aim of this work was to assess differences between two influenza seasons, the 2008-2009 A(H3N2) season and the 2009-2010 season with predominance of pandemic influenza virus circulation. Incidence rate (IR) of confirmed influenza illness were calculated for both periods and age group. Clinical presentation features by age group (0-4, 5-14, 15-64 and > 64 y.o.) were studied and compared for both seasons. Statistical significance of proportion differences assessed by statistic z and Mantel Hanzel's Woolf test. The level of statistical significance was established at alpha = 0.05. In both seasons studied, the 5-14 y.o. age group presented the highest confirmed influenza IR and highest presentation of cephalalgia as a symptom in the pandemic A(H1N1) 2009 season. In conclusion, the significant burden of influenza, both seasonal and pandemic, on children should encourage upgrading vaccination coverage in these age groups and especially for those included in risk groups for whom yearly vaccination is recommended.