A new blood test can help doctors quickly determine whether a baby’s fever results from a bacterial or viral infection, cutting down on unnecessary antibiotic prescriptions for newborns. The findings were shared at the European Emergency Medicine Congress, where they demonstrated the test’s accuracy in distinguishing between the two infection types in 60 infants treated at a pediatric emergency department in Genoa, Italy.
Fever in infants under three months old is considered a medical emergency because their immune systems remain underdeveloped. Physicians must then decide whether to administer antibiotics or simply monitor for a viral infection. Existing diagnostic methods frequently produce false positives, which can lead to excessive interventions such as lumbar punctures and extended hospital stays.
Tommaso Bellini, a pediatric emergency physician at IRCCS Istituto Giannina Gaslini, explained that the test detects two specific molecules present on white blood cells. The first, CD64, appears on neutrophils and increases during bacterial infections, while the second, CD169, is found on monocytes and rises sharply in viral cases. By combining these markers into a single ratio, the test can reliably differentiate between infection types.
In uninfected infants, the ratio averaged 1.10. Viral infections produced a ratio of 0.33, whereas bacterial infections resulted in an average of 16.22. The study reported 100% sensitivity and 96.6% specificity, confirming the test’s ability to correctly identify all bacterial cases and nearly all non-bacterial ones.
Maša Sorić, head of the emergency department in Zagreb, described the results as encouraging. She emphasized that parents often experience significant anxiety when their newborn develops a fever, and the test could help clinicians avoid overprescribing antibiotics for viral infections. The research team continues to recruit participants, with plans to expand testing to 75 additional infants before launching a larger trial involving 300 to 500 babies.
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