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 co-infection (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 1.514-7.757; 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.