This prospective cohort study was conducted at Hospital Universitari de Bellvitge, a 700-bed hospital in Barcelona, Spain. All non-immunosuppressed adults admitted to hospital with CAP via the emergency department from January 2013 to June 2016 were prospectively followed-up. Patients with immunosuppression were excluded from the study (e.g., chemotherapy, HIV infection, bone marrow or solid-organ transplantation, and systemic corticosteroid therapy).
For the purposes of this study, patients were split into sub-groups by age and the presence of comorbidity for comparison. For the age cut off, younger and older patients were classified as those aged <85 and ≥85 years old, respectively. The following individual comorbid conditions were considered: chronic cardiac disease, chronic obstructive pulmonary disease (COPD), diabetes mellitus, chronic kidney disease (CKD), and liver cirrhosis. Multimorbidity was defined as the presence of two or more of these chronic conditions.
Levels of the following inflammatory markers were measured at hospital admission: acute phase proteins (C-reactive protein [CRP] and procalcitonin [PCT]), cytokines (tumor necrosis factor-alpha [TNF-α], interleukin [IL]-6, and IL-10), and monocyte human leukocyte antigen DR (mHLA-DR) expression. The primary outcomes were the serum levels of inflammatory markers at hospital admission in each of the study groups.
Definitions and follow-up
CAP was defined as an acute illness with fever or hypothermia, cough with or without sputum production, dyspnea, altered breath sounds, pleuritic chest pain, and leukocytosis or leukopenia associated with a new infiltrate on a chest radiograph. At hospital admission, patients underwent a comprehensive clinical history and physical examination. If indicated by the attending physician, microbiological studies were performed, including two sets of blood cultures, including sputum Gram stain and culture when available, and urinary antigen detection for Legionella pneumophila and Streptococcus pneumoniae. Patients were stratified into risk class according to the Pneumonia Severity Index (PSI) [13] and were seen daily during admission by one or more of the investigators, who recorded clinical, laboratory and microbiological information. Empirical antibiotic treatment was applied according to hospital recommendations, typically using a β-lactam (ceftriaxone or amoxicillin/clavulanate) with or without a macrolide or a fluoroquinolone.
Regarding comorbid conditions, chronic heart disease was defined if there was evidence in clinical records or if the patient was receiving treatment for coronary artery disease, congestive heart failure, or arrhythmia, or if they had valvular heart disease [14]. COPD was defined as the coexistence of chronic and progressive symptoms such as dyspnea, cough, sputum, and airflow obstruction (diagnosed by spirometry), as described elsewhere [15]. A diagnosis of diabetes mellitus was made when the fasting plasma glucose concentration was ≥126 mg/dL on two or more separate occasions, or when a random plasma glucose ≥200 mg/dL was found in a patient with classic symptoms of hyperglycemia. Alternatively, the diagnosis was based on prior treatment with oral antidiabetic agents or insulin and/or clinical and/or a biochemical diagnosis of DM [16]. A patient was considered to have CKD if they had chronic renal disease and a glomerular filtration rate <60 mL/min/1.73 m2 or the need for chronic dialysis [17]. Finally, diagnosis of liver cirrhosis was made by histology and/or by clinical, laboratory, and imaging criteria, as described elsewhere [18].
Determination of biomarkers
Blood samples were taken from patients in the first 24 hours of hospital admission, centrifuged, and frozen at -80°C for later analysis. PCT, TNFα, IL-6, IL-10, and CRP levels were determined by using an enzyme immunoassay according to the manufacturer’s instructions. Monocyte HLA-DR expression was investigated on the same day, using a double-immunofluorescent whole-blood technique. At least 10,000 cells from each sample were analyzed on the flow cytometer.
Statistical analysis
Analysis of study variables was performed by SPSS Statistics for Windows, Version 17.0 (SPSS Inc., Chicago, USA). Continuous variables are described as median and interquartile range (IQR) and categorical variables are described as counts and percentages. To detect significant differences between study groups, we used the χ2 test or Fisher's exact test for categorical variables and the Student t-test or the Mann–Whitney U-test for continuous variables, as appropriate. All statistical analyses were specified before the data were seen. Statistical significance was accepted for two-tailed P-values of 0.05.