Background: 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).
Methods: 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.
Results: 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).
Conclusions: 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.
Keywords: Co-infection; Influenza; Intensive care; Outcome; Risk factors.