ICU-treated influenza A(H1N1) pdm09 infections more severe post pandemic than during 2009 pandemic: a retrospective analysis

BACKGROUND We compared in a single mixed intensive care unit (ICU) patients with influenza A(H1N1) pdm09 between pandemic and postpandemic periods. METHODS Retrospective analysis of prospectively collected data in 2009-2016. Data are expressed as median (25th-75th percentile) or number (percentile). RESULTS Seventy-six influenza A(H1N1) pdm09 patients were admitted to the ICU: 16 during the pandemic period and 60 during the postpandemic period. Postpandemic patients were significantly older (60 years vs. 43 years, p < 0.001) and less likely to have epilepsy or other neurological diseases compared with pandemic patients (5 [8.3%] vs. 6 [38%], respectively; p = 0.009). Postpandemic patients were more likely than pandemic patients to have cardiovascular disease (24 [40%] vs. 1 [6%], respectively; p = 0.015), and they had higher scores on APACHE II (17 [13-22] vs. 14 [10-17], p = 0.002) and SAPS II (40 [31-51] vs. 31 [25-35], p = 0.002) upon admission to the ICU. Postpandemic patients had higher maximal SOFA score (9 [5-12] vs. 5 [4-9], respectively; p = 0.03) during their ICU stay. Postpandemic patients had more often septic shock (40 [66.7%] vs. 8 [50.0%], p = 0.042), and longer median hospital stays (15.0 vs. 8.0 days, respectively; p = 0.006). During 2015-2016, only 18% of the ICU- treated patients had received seasonal influenza vaccination. CONCLUSIONS Postpandemic ICU-treated A(H1N1) pdm09 influenza patients were older and developed more often septic shock and had longer hospital stays than influenza patients during the 2009 pandemic.