Innate immune function and mortality in critically ill children with influenza: a multicenter study

Abstract

Objective: To prospectively evaluate relationships among serum cytokine levels, innate immune responsiveness, and mortality in a multicenter cohort of critically ill children with influenza infection.

Design: Prospective, multicenter, observational study.

Setting: Fifteen pediatric ICUs among members of the Pediatric Acute Lung Injury and Sepsis Investigators network.

Patients: Patients ≤18 yrs old admitted to a PICU with community-acquired influenza infection. A control group of outpatient children was also evaluated.

Interventions: ICU patients underwent sampling within 72 hrs of ICU admission for measurement of a panel of 31 serum cytokine levels and quantification of whole blood ex vivo lipopolysaccharide-stimulated tumor necrosis factor-α production capacity using a standardized stimulation protocol. Outpatient control subjects also underwent measurement of tumor necrosis factor-α production capacity.

Measurements and main results: Fifty-two patients (44 survivors, eight deaths) were sampled. High levels of serum cytokines (granulocyte macrophage colony-stimulating factor, interleukin-6, interleukin-8, interferon-inducible protein-10, monocyte chemotactic protein-1, and macrophage inflammatory protein-1α) were associated with mortality (p < 0.0016 for each comparison) as was the presence of secondary infection with Staphylococcus aureus (p = 0.007), particularly methicillin-resistant S. aureus (p < 0.0001). Nonsurvivors were immunosuppressed with leukopenia and markedly reduced tumor necrosis factor-α production capacity compared with outpatient control subjects (n = 21, p < 0.0001) and to ICU survivors (p < 0.0001). This association remained after controlling for multiple covariables. A tumor necrosis factor-α response <250 pg/mL was highly predictive of death and longer duration of ICU stay (p < 0.0001). Patients with S. aureus coinfection demonstrated the greatest degree of immunosuppression (p < 0.0001).

Conclusions: High serum levels of cytokines can coexist with marked innate immune suppression in children with critical influenza. Severe, early innate immune suppression is highly associated with both S. aureus coinfection and mortality in this population. Multicenter innate immune function testing is feasible and can identify these high-risk children.

Figure 1

Ex vivo tumor necrosis factor (TNF)-α production. A, Critically ill children with influenza infection (n = 52) demonstrated lower ex vivo TNF-α production capacity within the first 72 hrs of PICU stay compared with a cohort of children sampled in the outpatient phlebotomy department (n = 21) (p < 0.0001). B, Influenza nonsurvivors (n = 8) had markedly lower ex vivo TNF-α production capacity compared with those who survived (n = 44) (p < 0.0001). C, Subjects presenting with secondary infections resulting from Staphylococcus aureus (n = 11) demonstrated significantly reduced innate immune function compared with those with no bacterial coinfection (n = 34) and those with coinfection with other bacterial species (n = 7) (p = 0.001, analysis of variance [ANOVA]). Boxes represent median and interquartile range. Whiskers represent tenth to 90th percentile. ***p < 0.0001, *p < 0.05 vs. no bacteria, ^#p < 0.05 vs. other bacteria. MRSA = methicillin-resistant S. aureus; MSSA = methicillin-sensitive S. aureus

Figure 2

Ex vivo tumor necrosis factor (TNF)α production capacity, clinical outcomes, and relationship to absolute monocyte count. A, This assay demonstrated an outstanding capability to discriminate survivors from nonsurvivors within the first 72 hrs of PICU stay with an optimum cutoff point of 249 pg/mL. B, An ex vivo TNF-α production capacity >250 pg/mL was associated with faster time to ICU discharge (p = 0.0006). This remained significant after adjusting for Pediatric Risk of Mortality III score (p = 0.01). C, Lower ex vivo TNF-α production capacity was associated with a lower absolute monocyte count (AMC) (p = 0.002, r² = 0.23), although nine survivors (open circles) had AMCs as low as nonsurvivors (gray circles). Eight of these survivors had ex vivo TNF-α production capacity >250 pg/mL. AUC = area under the curve.