2009 H1N1 Compared to Post-pandemic H1N1 Influenza Among Pediatric Inpatients
The novel influenza A H1N1 strain emerged in 2009, contributing to significant morbidity and mortality. It is not known whether the current H1N1 strains cause the same severity of illness. The aim of this study was to compare the burden of disease from H1N1 influenza during the 2009 pandemic year to the subsequent years (2010-2014) and to identify whether the same risk factors for severe disease exist.
A retrospective cohort study of inpatients admitted to Children’s Hospital Colorado with respiratory specimens positive for influenza from May 1, 2009 to November 30, 2009, and Dec 1, 2010-April 12, 2014 was conducted. Data regarding patient demographics, clinical symptoms and signs, comorbidities and outcomes were compared to data previously obtained for the 2009 H1N1 pandemic influenza strain.
There were 328 inpatients with H1N1 during the 2009 pandemic, and 120 during the post-pandemic years. 90% of all post-pandemic H1N1 was observed during the 2013-2014 influenza season. 39% of patients with post pandemic H1N1 were completely vaccinated against influenza. Compared to the post-pandemic years, there were more Hispanic, black and native-American patients with H1N1 admitted (P <0.02 for all) and more patients with an underlying medical condition (P < 0.0001) during the pandemic year.
Older patients were more likely to be admitted to the ICU for both pandemic and post-pandemic groups (median age 6.5 years and 4.9 years respectively, P =0.19). For patients admitted to the ICU, there was higher antibiotic use during the pandemic year (82% vs 58%, P = 0.013). While a higher proportion of patients were admitted to the ICU during 2010-2014, 43/120 (36%) vs 84/328 (26%), P = 0.024, patients with 2009 H1N1 were more likely to be intubated (P = < 0.0001), have mental status changes (P= 0.0005), hypotension (P = 0.05) and have ARDS (P = 0.017) compared with the post-pandemic strain.
H1N1 represented the majority of influenza cases over the last influenza season. While there were higher rates of ICU admission among inpatients with post-pandemic H1N1, there appears to be decreased illness severity compared with the pandemic H1N1 patients, including lower intubation rates, hypotension, ARDS and mental status changes.
M. Cunningham, None
D. Curtis, Sanofi-Pasteur: Support for an Investigator-Initiated protocol, Research support
D. Bagdure, None
M. Glode, None
S. R. Dominguez, None