The Effect on Mortality of Bacterial Co-Infections on Critically Ill Patients with Community-Acquired COVID-19 and Influenza Pneumonia: A Systematic Review.

Bacterial co-infections in patients with viral pneumonia might increase mortality. In this study we aimed to evaluate their effect on the mortality of critically ill patients with viral pneumonia. A systematic search was conducted in PubMed, Web of Science, Scopus and Cochrane from inception until 30 March 2025. We included studies comparing the effect on mortality of bacterial co-infections in critically ill patients with viral pneumonia. The risk of bias was assessed by the Newcastle-Ottawa Scale. From 3643 studies, 10 were included in our study with a total of 2862 COVID-19 patients and 4573 influenza patients. Seven studies were retrospective and three prospective. In total, 359/2862 of the COVID-19 and 904/4573 of the influenza patients were co-infected. Co-infections increased mortality in five out of the six studies evaluating COVID-19 patients and in two out of the eight studies evaluating influenza patients. The majority of the included studies were retrospective, which may limit the accuracy of these results. The exclusion of non-English literature may have led to the omission of relevant data. Based on our results, the impact of bacterial co-infection may be more pronounced in patients with COVID-19 pneumonia admitted to the ICU than in patients with influenza pneumonia.