The contribution of bacterial co-infection to critical illness associated with 2009 influenza A (H1N1) [pH1N1] virus infection remains uncertain. The objective of this study was to determine if bacterial co-infection increased the morbidity and mortality of pH1N1.
Retrospective and Prospective cohort study
35 adult U.S. intensive care units over the course of one year
683 critically ill adults with confirmed or probable pH1N1
Measurements and Main Results
A confirmed or probable case was defined as a positive pH1N1 test result or positive test for influenza A that was otherwise not subtyped. Bacterial co-infection was defined as documented bacteremia or any presumed bacterial pneumonia with or without positive respiratory tract culture within 72 hours of ICU admission. The mean age was 45±16 years, mean BMI 32.5±11.1 kg/m2, and mean APACHE II score 21±9, with 76% having at least one co-morbidity. Of 207 (30.3%) patients with bacterial co-infection on ICU admission, 154 had positive cultures with Staphylococcus aureus (n=57) and Streptococcus pneumoniae (n=19) the most commonly identified pathogens. Bacterial co-infected patients were more likely to present with shock (21 vs. 10%; P=0.0001), require mechanical ventilation at the time of ICU admission (63 vs. 52%; P=0.005) and have longer duration of ICU care (median 7 vs. 6 days; P=0.05). Hospital mortality was 23%; 31% in bacterial co-infected patients and 21% in patients without co-infection (P=0.002). Immunosuppression (RR 1.57; 95% CI 1.20–2.06; P=0.0009) and Staphylococcus aureus at admission (RR 2.82; 95% CI: 1.76–4.51; P<0.0001) were independently associated with increased mortality.
Among ICU patients with pH1N1, bacterial co-infection diagnosed within 72 hours of admission, especially with Staphylococcus aureus, was associated with significantly higher morbidity and mortality.
Keywords: Pandemic H1N1 Influenza, Bacterial Co-infection, Critical Illness, Mortality