Increased incidence of co-infection in critically ill patients with influenza.

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Co-infection is frequently seen in critically ill patients with influenza, although the exact rate is unknown. We determined the rate of co-infection, the risk factors and the outcomes associated with co-infection in critically ill patients with influenza over a 7-year period in 148 Spanish intensive care units (ICUs). This was a prospective, observational, multicentre study. Influenza was diagnosed using the polymerase chain reaction. Co-infection had to be confirmed using standard bacteriological tests. The primary endpoint of this analysis was the presence of community-acquired co-infection, with secondary endpoints including ICU, 28-day and hospital mortality. Of 2901 ICU patients diagnosed with influenza, 482 (16.6%) had a co-infection. The proportion of cases of co-infection increased from 11.4% (110/968) in 2009 to 23.4% (80/342) in 2015 (P<0.001). Compared with patients without co-infection, patients with co-infection were older [adjusted odds ratio (aOR) 1.1, 95% confidence interval 1.1-1.2; P<0.001] and were more frequently immunosuppressed due to existing HIV infection (aOR 2.6 [1.5-4.5]; P<0.001) or preceding medication (aOR 1.4 [1.1-1.9]; P=0.03). Co-infection was an independent risk factor for ICU mortality (aOR 1.4 [1.1-1.8]; P<0.02), 28-day mortality (aOR 1.3 [1.1-1.7]; P=0.04) and hospital mortality (aOR 1.9 [1.5-2.5]; P<0.001). Co-infection in critically ill patients with influenza has increased in recent years. In this Spanish cohort, age and immunosuppression were risk factors for co-infection, and co-infection was an independent risk factor for ICU, 28-day and hospital mortality.