Critical illness from 2009 pandemic influenza A virus and bacterial coinfection in the United States*

Abstract

Objective 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. Design Retrospective and Prospective cohort study Setting 35 adult U.S. intensive care units over the course of one year Patients 683 critically ill adults with confirmed or probable pH1N1 Interventions None 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. Conclusions 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.

Co-infection in severe influenza: a new epidemiology?

“…It is highly probable that the mechanism explaining the higher mortality is due to either to the bacterial infection itself or to an association of virulence factors from both virus and bacteria. Lastly, as shown in this paper and others, the epidemiology of pathogens responsible for co-infection is regional and likely depends on many local factors, but may also be subject to change over time, with emergence in the community of pathogens usually seen in nosocomial infections [6,7,9,12].…”

“…Similar to previously reported data from this group [5], Streptococcus pneumoniae was the predominant pathogen recovered, followed by Pseudomonas aeruginosa and methicillin-susceptible Staphylococcus aureus (MSSA). Not unexpectedly, data from the USA found that S. aureus was the predominant organism, with a higher prevalence of methicillin-resistant S. aureus (MRSA) [6]. Interestingly, the authors found an apparent increased rate of co-infection over time (from 11.4% in 2009 to 23.4% in 2015), without clear explanation.…”

“…Although this was previously demonstrated in several studies, this is the largest study published to date that confirms this association. Rice at al., found, in 2012, that among 683 patients with influenza A H1N1 infection, bacterial co-infection was frequent (30.3%) and associated with higher mortality rate as compared to patients without [6]. In a more recent study on 507 ICU patients, Shah at al., found a 22.5% rate of bacterial co-infection and a similar association between bacterial co-infection and death [12].…”

“…The choice of the initial antimicrobial treatment should be based on the local and national epidemiology and target pathogens responsible for CAP: in France and northern Europe, S. pneumoniae and methicillin-susceptible S. aureus seem to be the predominant pathogens. In the USA, the high incidence of methicillin-resistant S. aureus should be taken into account for the initial choice of antibiotics [6]. If P. aeruginosa incidence is increasing over time (which remains to be confirmed in further studies), it may also need empiric antimicrobial coverage since it may have an impact on overall mortality.…”

Staphylococcus aureus colonization and non-influenza respiratory viruses: Interactions and synergism mechanisms

“…During the 2009 A/H1N1 influenza pandemic, bacterial co-infections complicated up to one-third of influenza cases in the United States in which S. aureus was the most common pathogen, accounting for 27% of the cases in both critically ill children and adults [25,26]. S. aureus co-infection was associated with significantly higher morbidity and mortality [26]. To date, the clinical association between the healthy carriage of S. aureus and the secondary staphylococcal pneumonia is still unclear.…”