Background 

Improved tools are required to detect bacterial infection in children with fever without source (FWS), especially when younger than 3 years old. The aim of the present study was to investigate the diagnostic accuracy of a host signature combining for the first time two viral-induced biomarkers, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and interferon γ-induced protein-10 (IP-10), with a bacterial-induced one, C-reactive protein (CRP), to reliably predict bacterial infection in children with fever without source (FWS) and to compare its performance to routine individual biomarkers (CRP, procalcitonin (PCT), white blood cell and absolute neutrophil counts, TRAIL, and IP-10) and to the Labscore.

Methods

This was a prospective diagnostic accuracy study conducted in a single tertiary center in children aged less than 3 years old presenting with FWS. Reference standard etiology (bacterial or viral) was assigned by a panel of three independent experts. Diagnostic accuracy (AUC, sensitivity, specificity) of host individual biomarkers and combinatorial scores was evaluated in comparison to reference standard outcomes (expert panel adjudication and microbiological diagnosis). 

Results

241 patients were included. 68 of them (28%) were diagnosed with a bacterial infection and 5 (2%) with invasive bacterial infection (IBI). Labscore, ImmunoXpert, and CRP attained the highest AUC values for the detection of bacterial infection, respectively 0.854 (0.804–0.905), 0.827 (0.764–0.890), and 0.807 (0.744–0.869). Labscore and ImmunoXpert outperformed the other single biomarkers with higher sensitivity and/or specificity and showed comparable performance to one another although slightly reduced sensitivity in children < 90 days of age.

Conclusion

Labscore and ImmunoXpert demonstrate high diagnostic accuracy for safely discriminating bacterial infection in children with FWS aged under and over 90 days, supporting their adoption in the assessment of febrile patients.

Study Design: Prospective diagnostic accuracy study in children with FWS aged less than 3 years old (consecutive sample), performed in the pediatric emergency department (PED) of a single Swiss tertiary center from November 2015 to January 2018, using expert panel adjudication and microbiological diagnosis as diagnostic reference standards. 

Primary objective: To prospectively investigate the diagnostic accuracy of a host signature (TRAIL, IP-10, and CRP) to reliably predict bacterial infections and to compare its performance to routine individual biomarkers (CRP, PCT, WBC, ANC, TRAIL, and IP-10) and to the Labscore.

Secondary objectives: To compare the diagnostic accuracy of the ImmunoXpert, the Labscore, and individual biomarkers to reliably predict IBI.

Participants: Patients aged less than 3 years old presenting to the PED with FWS after a thorough history and physical exam were eligible.  Exclusion criteria were comorbidities predisposing to infections such as cancer, primary or secondary immunodeficiency, and iatrogenic immunosuppression.

Study Procedure: After informed consent was obtained, patients’ clinical characteristics were recorded (age, sex, delay between fever onset and presentation, maximum temperature before presentation). Patients were assessed with white blood cell count (WBC), absolute neutrophil count (ANC), band count, CRP, PCT, urinary dipstick and culture, and blood culture. Additional testing (CSF culture, chest X-ray, synovial fluid or stool culture, etc.) was optional. An additional 0.6 mL sample was drawn, dedicated to the determination of CRP, TRAIL and IP-10 and the ImmunoXpert score. A group of 50 healthy Canadian children from trauma and dental clinics served as control patients to assess the differential expression of biomarkers and combinatorial scores between patients with fever without source and children with no fever and no current infection. The study was approved by the Institutional Ethics Committee (Cantonal Committee on Ethics in Scientific Research of Geneva, CCER), adheres to STARD 2015 guidelines, and is registered under ClinicalTrials.gov (NCT03224026). No investigation was performed before signature of a written informed consent. The use of sera from control patients was approved by Toronto’s Hospital for Sick Children Ethics Committee. 

Blinding process: Experts had access to full medical records but were blinded to the diagnosis of their peers and to TRAIL, IP-10 and ImmunoXpert results; CRP, PCT and urinary dipstick data were available to the experts. The ImmunoXpert test was performed on anonymized samples, and performers/readers of the index tests had no access to clinical information and reference standard results. The index test and panel expert reference standard outcomes were locked prior to unblinding at the end of the recruitment phase.