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

We compared in a single mixed intensive care unit (ICU) patients with influenza A(H1N1) pdm09 between pandemic and postpandemic periods.

Retrospective analysis of prospectively collected data in 2009–2016. Data are expressed as median (25th–75th percentile) or number (percentile).

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.

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.