New Blood Test Distinguishes Bacterial from Viral Fever in Infants
A diagnostic blood test can accurately distinguish between serious bacterial infections and self-limiting viral illnesses in infants under three months of age presenting with a fever, according to research presented. Developed to address a major diagnostic dilemma in paediatric emergency care, the flow cytometry technique quantifies two specific molecular markers on white blood cells to help clinicians rule out severe bacterial infections and avoid unnecessary hospital admissions, invasive lumbar punctures, and antibiotic overtreatment.
- The test measures CD64 on neutrophils and CD169 on monocytes, combining them into a single ratio that separates bacterial infections from viral illnesses with high accuracy.
- In an initial cohort of 60 infants evaluated at IRCCS Istituto Giannina Gaslini, the assay demonstrated a sensitivity of 100 percent and a specificity of 96.6 percent.
- Researchers have initiated a broader multicenter, prospective trial known as DISCERN to validate these findings across 300 to 500 babies.
The Diagnostic Dilemma of Fever in Early Infancy
A fever in a baby under three months of age is considered a medical emergency. Because very young infants possess undeveloped immune systems, an infection can rapidly become life-threatening. In the emergency department, clinical staff face the critical task of assessing febrile infants to differentiate between severe bacterial infections that demand immediate antibiotic therapy and viral infections that typically resolve with supportive monitoring and care.
Dr. Tommaso Bellini, a paediatric emergency physician at the IRCCS Istituto Giannina Gaslini in Genoa, Italy, outlined the clinical challenge. Standard biomarkers currently in use can indicate the presence of a bacterial infection, but they frequently generate false positives. These false positives drive overtreatment, subjecting infants to unnecessary lumbar punctures, hospital admissions, and courses of antibiotics when they are suffering only from a self-limiting virus.
Flow Cytometry and Dual-Molecule Ratio Analysis
To improve diagnostic accuracy, Dr. Bellini and his colleagues conducted research involving 60 babies brought to the paediatric emergency department of IRCCS Istituto Giannina Gaslini, encompassing infants assessed for fever as well as others evaluated for non-infectious conditions. The research team collected blood samples from all participants and analyzed them using flow cytometry, an advanced laboratory technique that permits the detailed study of individual cells.
The assay quantifies the levels of two specific molecules that increase in response to different types of pathogens. CD64 is located on the surface of neutrophils, a category of white blood cell, and increases in response to bacterial infections. CD169 is located on the surface of monocytes, another type of white blood cell, and increases in response to viral infections.
By combining measurements of both molecules into a single ratio for each infant, researchers found clear statistical separation between patient groups. Babies with no infection registered an average ratio score of 1.10. Those confirmed to have a viral infection showed an average score of 0.33, while infants confirmed to have a bacterial infection averaged 16.22. The diagnostic tool achieved a sensitivity of 100 percent, successfully identifying all cases of bacterial infection, and a specificity of 96.6 percent, yielding a minimal rate of false positives.
Dr. Bellini noted that these two marker molecules display opposing biological signatures, where one rises while the other falls depending on the pathogen type. While the initial results from the 60-infant cohort are promising, the assay currently relies on specialized flow cytometry equipment and trained laboratory staff, precluding its use as a standard bedside test outside of specialist facilities. Translating the method into a fast, low-cost, point-of-care format remains the primary research objective.
Broader Implications for Antibiotic Stewardship
The research is expanding to incorporate data on 75 babies and forms the foundation for a larger multicentre, prospective investigation titled DISCERN, an acronym for Discriminating Infection via Surface CD-marker Expression Ratios iN infancy. This upcoming trial aims to evaluate the diagnostic accuracy of the test in 300 to 500 infants.
Dr. Maša Sorić, head of the emergency department at University Hospital Merkur in Zagreb, Croatia, and a member of the European Society for Emergency Medicine (EUSEM) abstract selection committee, emphasized the emotional toll that infant fevers place on families. She noted that emergency departments must treat every case as potentially serious until proven otherwise, which frequently entails invasive testing, empirical antibiotics, and prolonged hospital stays.
Commenting on the potential impact of the research if validated in larger trials, Dr. Sorić stated that the approach could provide a reliable method to identify which infants require antibiotics and which do not. This capability could reduce unnecessary medical interventions and address the broader public health challenge of antimicrobial resistance driven by the overuse of antibiotics, thereby helping to preserve the clinical efficacy of vital medications.
Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.