A new diagnostic blood test measuring the levels of two specific molecular markers can accurately distinguish between bacterial and viral infections in febrile newborn babies, according to research presented at the European Emergency Medicine Congress. Developed by pediatric emergency physicians in Italy, the method relies on flow cytometry to analyze cell surface proteins, potentially offering a way to reduce unnecessary antibiotic treatments and hospital admissions for infants.
Diagnostic Dilemma in Febrile Newborns
Fever in babies under three months of age represents a medical emergency. Undeveloped immune systems mean that infections can quickly become life-threatening for infants in this age group.
Emergency department staff must rapidly assess these patients to separate serious bacterial infections requiring antibiotics from viral infections that typically resolve with monitoring and care. However, standard biomarkers often produce false positives, leading to overtreatment. According to Dr. Tommaso Bellini, a pediatric emergency physician at the IRCCS Istituto Giannina Gaslini in Genoa, Italy, this diagnostic uncertainty drives unnecessary lumbar punctures, antibiotic administration, and hospital admissions for infants who ultimately have only a viral illness.
Flow Cytometry and Dual-Molecule Ratios
To address this clinical challenge, Dr. Bellini and his research colleagues at the IRCCS Istituto Giannina Gaslini analyzed blood samples from 60 infants brought to the pediatric emergency department. The cohort included babies being assessed for fever alongside others being evaluated for non-infectious conditions.
Researchers used flow cytometry—an advanced laboratory technique that examines individual cell characteristics—to quantify two specific surface molecules on white blood cells:
- CD64: Located on the surface of neutrophils, this molecule increases in response to bacterial infections.
- CD169: Found on monocytes, this molecule increases during viral infections.
By combining these measurements into a single ratio, the test demonstrated distinct numerical signatures for different clinical statuses. Babies with no infection showed an average ratio score of 1.10. Those with confirmed viral infections averaged 0.33, while infants with confirmed bacterial infections averaged 16.22.
The initial evaluation yielded a sensitivity of 100%, meaning it successfully identified every bacterial infection case, and a specificity of 96.6%, indicating an extremely low rate of false positives.
Clinical Implications and Antimicrobial Resistance
Dr. Maša Sorić, head of the emergency department at University Hospital Merkur in Zagreb, Croatia, and a member of the EUSEM abstract selection committee who was not involved with the study, noted the emotional toll on families. She explained that emergency staff must treat every infant fever as potentially serious until proven otherwise, which currently entails invasive tests and prolonged hospital stays.
“If these results can be reinforced in a larger trial, they could mean that we have a much better way of knowing which babies probably have a bacterial infection that needs antibiotics, and which babies probably do not,” Dr. Sorić said.
Dr. Sorić also highlighted the broader implications for public health, pointing out that minimizing unnecessary antibiotic use helps curb the growth of antimicrobial resistance and preserves the effectiveness of vital medications.
Next Steps and the DISCERN Study
While the initial findings from the 60-baby cohort are promising, the assessment currently depends on flow cytometry, requiring specialized equipment and trained staff. It is not yet a bedside point-of-care test widely available outside specialist laboratories.
Dr. Bellini stated that translating the assay into a fast, low-cost point-of-care format is the team’s primary technical goal. Meanwhile, data collection is expanding to a total of 75 babies in the current cohort. The research group has initiated a larger, multicenter prospective trial named DISCERN (Discriminating Infection via Surface CD-marker Expression Ratios iN infancy), which will evaluate the accuracy of the test across 300 to 500 infants.
Infant Fever Testing Details
Did you know? During a viral infection, expression of the CD169 molecule rises while CD64 drops. During a bacterial infection, the exact reverse occurs, allowing researchers to combine both markers into a highly accurate single ratio.
New blood test measures CD64 and CD169 ratios to identify infections
Why is a fever in a newborn considered a medical emergency?
Babies under three months of age possess undeveloped immune systems, meaning bacterial infections can escalate and become life-threatening very quickly.
How does the new blood test differentiate between bacterial and viral infections?
The test uses flow cytometry to measure levels of CD64 on neutrophils (which rise during bacterial infections) and CD169 on monocytes (which rise during viral infections) and combines them into a single ratio.
Is this test currently available in hospital emergency departments?
Not yet. The method currently requires specialized laboratory equipment and trained staff, though researchers are working toward developing a fast, low-cost point-of-care format.
What is the DISCERN study?
DISCERN is a larger, multicenter prospective trial designed by Dr. Tommaso Bellini and colleagues to assess the diagnostic accuracy of the CD-marker ratio test in 300 to 500 infants.
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