Background
This study analyzes frequency of ventilator associated pneumonia (VAP), pulmonary aspergillus infections, and viral reactivations in patients with ARDS treated with VV-ECMO due to COVID-19 or Influenza. 

Methods
Retrospective analysis of all consecutively patients at the University Hospital Regensburg requiring VV-ECMO due to COVID-19 (March 2020 - May 2022) or Influenza (May 2012 - December 2022). 

Results
147 patients (age (median [IQR]) 55.3 [48.7 ? 61.7], SOFA at VV-ECMO initiation 9 [8 ? 12], 23 [14 ? 38] days on VV-ECMO) suffering from COVID-19 and 72 influenza patients (age 55.3 [46 ? 61.3], SOFA at VV-ECMO initiation 13 [10 ? 15], 16 [10 ? 23] days on VV-ECMO) were included in the analysis. Pulmonary superinfections were more frequent in COVID-19 than in influenza (VAP: 61% vs. 39%, pulmonary Aspergillosis: 33% vs. 22%, CMV reactivation: 19% vs. 4%, HSV reactivation: 49% vs. 26). irst episode of VAP in COVID-19 and Influenza was detected 2 days [1 ? 15] after and 1 day (-3 ? 22) before ECMO initiation, respectively. First VAP-episode in COVID-19 were mainly caused by Klebsiella spp. (29%,), Staphylococcus aureus (27%) and E. coli (11%). Further VAP-episodes (30% in COVID-19) and relapses of VAP were mainly caused by Klebsiella spp. (53%, 64%, respectively). In Influenza, VAP was mainly caused by Staphylococcus aureus (28%) and Streptococcus pneumoniae (28%), further VAP episodes were not observed.

Conclusion
Superinfections were common in patients treated with VV-ECMO and occur more frequently in COVID-19 ARDS compared to Influenza. VAP occurs early and may significantly contribute to the need of VV-ECMO. Thus, a meticulous micorbiologic workup is advisable.