Background: Although secondary infections are recognized as a cause of morbidity and mortality in seasonal influenza, their frequency, characteristics, and associated clinical outcomes in 2009 influenza A(H1N1) (A[H1N1])-related critical illness are unknown.
Methods: In a prospective cohort of adult patients admitted to Canadian ICUs with influenza A(H1N1) infection, the frequency and associated clinical outcomes of prevalent (culture taken within 72 h of ICU admission) and ICU-acquired (culture taken after 72 h from ICU admission) positive bacterial cultures were determined.
Results: Among 681 patients, the mean age was 47.9 years (SD, 15.1), APACHE (Acute Physiology and Chronic Health Examination) II score was 21.0 (9.9), and 573 patients (84.0%) were invasively mechanically ventilated. Positive cultures were obtained in 259 patients (38.0%): 77 (29.7%) had prevalent, 115 (44.4%) had ICU-acquired, and 40 (15.4%) had both; culture date was unavailable in 27 (10.4%). The most common bacterial organisms isolated were coagulase-negative staphylococci, Staphylococcus aureus, Pseudomonas species, and Streptococcus pneumoniae. Antibiotics were prescribed in 661 (97.1%), with 3.8 (1.9) prescriptions per patient. Patients with any positive culture had longer days of mechanical ventilation (mean [SD], 15.2 [10.7] vs 10.7 [9.0]; P<.0001), ICU stay (median [interquartile range (IQR)], 18.2 [12.5] days vs 10.8 [9.0] days, P<.0001), and hospitalization (median [IQR], 30.7 [20.7] days vs 19.2 [17.4] days, P<.0001) and a trend toward increased hospital mortality (25.1% vs 19.9%, P=.15). Patients with ICU-acquired positive cultures had worse outcomes compared with those with positive prevalent cultures or who were culture-negative.
Conclusion: Culture-based evidence of secondary infections commonly complicates A(H1N1)-related critical illness and is associated with worse clinical outcomes despite nearly ubiquitous antibiotic administration.