Community-acquired bacterial co-infection predicts severity and mortality in influenza-associated pneumonia admitted patients

Background: Influenza is frequently complicated by bacterial co-infection, causing additional hospitalization and mortality. We determined the incidence, risk factors and outcomes of patients with influenza-associated community-acquired bacterial co-infection. Method: This was a retrospective, observational study. Influenza was diagnosed using the polymerase chain reaction. Co-infection had to be confirmed using standard bacteriological tests. The primary endpoint was presence of community-acquired co-infection, and the secondary endpoint was in-hospital mortality. Results: During the 8 influenza seasons from 2010 to 2018, of the 209 influenza-associated pneumonia admitted patients, 41 (19.6%) were identified with community-acquired bacterial co-infections and Staphylococcus aureus was the predominant strain. Compared with patients without co-infection, patients with co-infection had similar demographic characteristics and co-morbidities, obtained a higher APACHE II score and a higher SOFA score, and had higher ratio of sepsis shock, invasive mechanical ventilation, and ICU requirement. In-hospital mortality independently associated with bacterial coinfection (adjusted hazard ratio (aHR) 2.619; 95% CI 1.252-5.480; p = 0.011); in subgroup S. aureus (aHR 6.267; 95% CI 2.679-14.662; p < 0.001) and other pathogens (aHR 2.964; 95% CI 1.160-7.577; p = 0.023); and in subgroup positive findings in bloodstream (aHR 7.420; 95% CI 2.712-20.302; p < 0.001) and positive findings in other site (aHR 3.427; 95% CI 1.514e7.757; p = 0.003). Conclusion: Community-acquired bacterial co-infection was frequent in influenza-associated pneumonia, without risk factor identified yet. Bacterial co-infection was likely to predict severity, and was an independent risk factor for in-hospital mortality. Co-infection of Staphylococcus aureus with influenza was identified as a lethal synergism, and should be targeted when developing clinical antibiotic strategies. (c) 2018 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.