Age-related differences of outcomes in patients hospitalized with community-acquired pneumonia are not explained by differences in immune response

Introduction

We hypothesized that the higher risk of severe sepsis and mortality observed after infection in prior epidemiologic studies are due to age-related differences in immune response.

Methods

We analyzed 2,183 subjects from a multicenter observational cohort of patients hospitalized with community-acquired pneumonia (CAP). We divided subjects into five age groups (<50, 50 to 64, 65 to 74, 74 to 84, ≥85). To compare immune response, we measured circulating inflammatory (IL-6 and IL-10), coagulation-fibrinolysis (D-dimer, factor IX (F-IX), thrombin-antithrombin complex (TAT), antithrombin (AT) and plasminogen-activator inhibitor (PAI)), and cell surface markers (TLR2, TLR4, HLADR) on emergency department (ED) presentation and during the first week of hospitalization.

Results

Older subjects had higher rates of severe sepsis (14.8%, 23.0%, 26.3%, 34.0%, 42.3%) and 90-day mortality (1.8%, 3.8%, 9.2%, 18.2%, 19.8%, per age group (P < 0.001)). However, there were no age-related differences in inflammatory or cell surface markers and only modest differences in coagulation-fibrinolysis abnormalities on ED presentation and over the first week (P < 0.05) (Figure 1).

Figure 1

Modest differences in circulating concentration of coagulation-fibrinolysis markers on ED presentation (day 1) and over the first 7 days. P¹, day 1 P value from ANOVA model adjusted for sex, race, co-morbidity, and smoking status; Tobit models used for censored data. P², day 1 to 7 P value from mixed effects model adjusted for sex, race, co-morbidity, and smoking status; Tobmit models used for censored data.

Conclusions

Despite large differences in outcomes, patients hospitalized with CAP displayed no age-related differences in circulating inflammatory or cell surface markers and modest differences in circulating coagulation-fibrinolysis markers.