The Prevalence and the Impacts of Pulmonary Bacterial Coinfections and Secondary Bacterial Pneumonia in Patients with Severe Influenza Pneumonitis

Abstract Background: This study investigated the prevalence and clinical outcomes of pulmonary bacterial coinfections and secondary bacterial pneumonia in patients with severe influenza pneumonitis. The causative pathogens and their clinical impacts were analyzed. Methods: We retrospectively analyzed the data of adult patients with severe influenza pneumonitis admitted to our medical ICUs from January 2014 to May 2018. Bacterial confection (in first 48 h) and secondary bacterial pneumonia (from 48 h to 1 week) were confirmed by chest radiographs and positive findings in the respiratory specimen obtained from lower airway. The risk factors of pulmonary coinfection were evaluated. The outcomes of patients with or without pulmonary coninfection or secondary bacterial pneumonia were also analyzed.Results: We identified 117 critically ill patients with laboratory-confirmed influenza pneumonitis admitted to the medical ICUs. Klebsiella pneumoniae (31.4%) and Staphylococcus aureus (22.8%) were the most commonly identified bacteria in patients with bacterial coinfection. A high proportion of methicillin-resistant Staphylococcus aureus was noted. Liver cirrhosis and diabetes mellitus were the independent risk factors for bacterial coinfection. Acinetobacter baumannii (28%) and S. aureus (25%) were the most often identified bacteria in patients with secondary bacterial pneumonia. Patients with secondary bacterial pneumonia had longer period of mechanical ventilation, longer ICU stay and hospital stay, and higher mortality.Conclusions: Bacterial coinfection or secondary infection in patients with severe influenza pneumonitis were associated with higher rates of morbidity and mortality in ICU patients. Earlier diagnosis and appropriate therapy, especially in patients with liver cirrhosis and diabetes mellitus, should be cautiously considered.