When a fever arrives in an infant too young to speak, medicine has long been forced to choose between doing too much and risking too little. Researchers in Genoa have now identified a two-molecule blood ratio that may finally give clinicians a reliable way to distinguish bacterial danger from viral passage in babies under three months old — a distinction that carries consequences measured in lumbar punctures, antibiotic courses, and days spent apart from parents. The finding is small in scale but large in implication, pointing toward a future where diagnostic precision, not precautionary exces
Two-molecule blood test shows promise in distinguishing bacterial from viral infections in febrile infants
Febrile infants under three months face life-threatening risks from untreated bacterial infections, while current diagnostic approaches subject many to unnecessary invasive procedures and antibiotics.
A fever in a baby under three months is a medical emergency
Mark
So the test measures two molecules in the blood. How do we know those molecules actually tell us what kind of infection a baby has?
Mimi
They're markers that respond to infection. CD64 goes up when bacteria are present, CD169 when viruses are. The researchers found that the ratio between them separates the two cleanly in their 60 babies.
Luke
But 60 babies is small. And we're relying on the assumption that these molecules behave the same way in every infant. What if they don't? What if the ratio works in Italian babies but not in others?
Mimi
That's exactly why they're running DISCERN—a 300 to 500 baby study across multiple centers. You need the larger trial to know if this holds up.
Mark
The test caught every bacterial infection. That's 100 percent. Why isn't that enough?
Luke
Because 100 percent sensitivity in 60 babies doesn't guarantee 100 percent in 500. And we still need to know: how fast is the test? If it takes hours to run, it doesn't help a parent in the emergency department at 2 a.m.
Mimi
Right now it requires flow cytometry equipment and trained staff. That's the bottleneck. The goal is to make it a bedside test, but that hasn't happened yet.
Mark
So the real promise is conditional on two things: the larger trial confirming the findings, and someone figuring out how to make it fast and cheap.
Mimi
Exactly. The science looks solid. The translation to clinical practice is still ahead.
Luke
And we should note: the current standard biomarkers do catch infections. They just generate false positives. This test might reduce those false positives, but it's not like the current approach is useless.
Mark
It's an improvement, not a revolution.
Mimi
An improvement that could spare a lot of babies unnecessary procedures. That matters.
O Pulso
- Febrile infants under three months occupy one of medicine's most anxious thresholds — too young for their immune systems to be trusted, too fragile for clinicians to wait and see.
- Today's standard blood markers cast too wide a net, triggering invasive procedures like lumbar punctures and unnecessary antibiotic courses for babies who carry only a virus.
- A team at IRCCS Istituto Giannina Gaslini measured the ratio of two molecules — CD64, which rises with bacteria, and CD169, which rises with viruses — and found the numbers separated cleanly: bacterial infections averaged 16.22, viral just 0.33.
- The test achieved 100% sensitivity and 96.6% specificity across 60 infants, catching every bacterial case while generating almost no false alarms.
- The obstacle now is infrastructure: flow cytometry requires specialized labs, not emergency bedsides, so the team is racing to build a fast, low-cost point-of-care version.
- A multicentre trial called DISCERN, enrolling 300 to 500 infants, is set to determine whether this precision holds when tested against the full complexity of the real world.
When a fever arrives in an infant too young to speak, medicine has long been forced to choose between doing too much and risking too little. Researchers in Genoa have now identified a two-molecule blood ratio that may finally give clinicians a reliable way to distinguish bacterial danger from viral passage in babies under three months old — a distinction that carries consequences measured in lumbar punctures, antibiotic courses, and days spent apart from parents. The finding is small in scale but large in implication, pointing toward a future where diagnostic precision, not precautionary excess, guides the earliest and most vulnerable encounters with illness.
A fever in a baby under three months old is one of medicine's most urgent uncertainties. Bacterial infections in infants can escalate with terrifying speed, yet the tools doctors currently use to detect them are imprecise — generating false positives that send many babies through lumbar punctures, antibiotic courses, and hospital stays they never needed. The cost falls on families and on infants who had only a virus.
Dr. Tommaso Bellini and colleagues at IRCCS Istituto Giannina Gaslini in Genoa approached the problem through flow cytometry, analyzing blood samples from 60 infants to examine two molecules with opposing responses to infection. CD64, found on neutrophils, climbs in the presence of bacteria. CD169, found on monocytes, rises with viruses. By calculating their ratio, the team found a striking separation: uninfected infants averaged 1.10, viral cases 0.33, and bacterial cases 16.22.
The test identified every bacterial infection in the cohort — 100% sensitivity — while misclassifying only 3.4% of non-bacterial cases, a specificity of 96.6%. The diagnostic signal was unusually clean for such a difficult clinical question.
The path from lab to bedside remains the central challenge. Flow cytometry demands specialized equipment and trained staff, placing it beyond the reach of most emergency departments. Bellini's team is now working to compress the method into a rapid, affordable point-of-care format. The study will expand to 75 infants before feeding into DISCERN, a multicentre trial enrolling 300 to 500 babies designed to confirm whether the ratio's precision survives contact with broader, messier clinical reality.
For clinicians like Dr. Maša Sorić of University Hospital Merkur in Zagreb, who observed the research from outside, the stakes are clear. Every feverish newborn must be treated as potentially serious until the evidence says otherwise. A validated two-molecule test could change that calculus — fewer invasive procedures, fewer unnecessary antibiotics, shorter separations between frightened parents and their smallest patients.
A fever in a baby under three months old sends parents to the emergency department in genuine fear. In infants whose immune systems are still forming, an infection can turn dangerous with alarming speed. But once they arrive, doctors face a diagnostic puzzle: how to tell which babies have a bacterial infection that demands immediate antibiotics, and which have a viral illness that will resolve on its own with time and care.
The standard tools available today—blood markers that signal infection—cast a wide net. They catch real bacterial infections, yes, but they also generate false alarms. A positive result can trigger a cascade of interventions: lumbar punctures to check for meningitis, courses of antibiotics, days in the hospital. Many of these babies, it turns out, had only a virus. The cost is real: unnecessary procedures, unnecessary drugs, unnecessary separation from parents.
Researchers at IRCCS Istituto Giannina Gaslini in Genoa, Italy, led by pediatric emergency physician Dr. Tommaso Bellini, set out to build something more precise. They collected blood samples from 60 infants—some with fever, some with other conditions—and analyzed them using flow cytometry, a technique that lets researchers examine individual cells in detail. They focused on two molecules known to respond to infection. CD64 appears on neutrophils, a type of white blood cell, and rises when bacteria are present. CD169 sits on monocytes, another white blood cell type, and increases in response to viruses. The two molecules tell opposite stories.
Bellini's team calculated a simple ratio of these two markers for each baby. The numbers told a stark story. Babies with no infection averaged a ratio of 1.10. Those confirmed to have viral infections averaged 0.33. Those with bacterial infections averaged 16.22. The separation was clean. The test caught every single case of bacterial infection—a sensitivity of 100 percent. False positives, where the test suggested bacterial infection when there was none, occurred in only 3.4 percent of cases. A specificity of 96.6 percent.
The catch is practical. The test currently requires flow cytometry equipment and trained technicians. It is not something an emergency department can run at the bedside. It lives in specialized labs, not widely available. Bellini and his colleagues are now working to translate it into something faster and cheaper, a point-of-care test that could be deployed where babies actually arrive with fever. The initial study will expand to 75 infants. A larger trial called DISCERN is beginning, enrolling 300 to 500 babies across multiple centers to confirm the findings hold up in the real world.
Dr. Maša Sorić, head of emergency medicine at University Hospital Merkur in Zagreb and not involved in the research, sees the potential clearly. For parents, she notes, bringing a feverish newborn to the hospital is an ordeal of worry. Every case must be treated as serious until proven otherwise. If a larger trial confirms what this small study suggests—that a two-molecule ratio can reliably separate bacterial from viral infection—the implications ripple outward. Fewer unnecessary lumbar punctures. Fewer courses of antibiotics given to babies who do not need them. Shorter hospital stays. A better way to know, with confidence, which infants truly need aggressive treatment and which simply need time.
Citações Notáveis
In very young babies with fever, distinguishing serious bacterial infection from self-limiting viral illness is a major diagnostic dilemma. Our standard biomarkers can help show when there might be a bacterial infection, but they also create false positives, which drives overtreatment.— Dr. Tommaso Bellini, pediatric emergency physician, IRCCS Istituto Giannina Gaslini
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. Maša Sorić, head of emergency department, University Hospital Merkur
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