A blood test that can determine whether a feverish baby has a bacterial or viral infection in just 15 to 20 minutes has been developed by researchers, offering a rapid way to assess whether an infection is serious or may resolve without treatment. The test, which measures levels of two proteins in the blood, could help doctors avoid giving antibiotics unnecessarily and slow the spread of drug resistance.
When babies are brought to hospital with a fever, they are considered high-risk until proven otherwise, according to Tommaso Bellini at the Giannina Gaslini Institute in Genoa, Italy, who led the research. Fever can be caused by viruses or bacteria, which require different medications. Most common viruses are fairly benign, while bacterial infections are generally more dangerous. Existing tests to identify the type of infection take at least a few hours, so babies with fever are often given antibiotics as a precaution. However, only about 15 per cent of them actually have a serious bacterial infection, and this unnecessary use of antibiotics contributes to bacterial resistance.
To develop the rapid test, Bellini and his colleagues followed 85 babies, all younger than 90 days old, who were brought to emergency rooms with fever and had no previous serious health concerns. The team took blood samples and tested for two proteins: CD64 and CD169. Previous studies have shown that these proteins become more common in certain blood cells when the body responds to infections. CD64 is produced at higher levels in response to bacteria and is found on the surface of white blood cells called neutrophils. CD169 rises in response to viruses and appears on the outer membranes of monocytes, another type of white blood cell.
By comparing the levels of both proteins in neutrophils and monocytes, the test correctly identified all 15 cases of bacterial infection, 44 cases of viral infection and 26 cases of no infection. Bellini presented the results at the European Emergency Medicine Congress in Paris, France. The results came through in 15 to 20 minutes in a lab, and Bellini is now working on a version that can be used as quickly in hospitals.
The research builds on several years of work to develop a CD64/CD169 test. Fabrice Malergue at Beckman Coulter Life Sciences in Marseille, France, has spent much of the past decade working on it. In 2021, his team found that CD64 and CD169 levels reliably distinguish between bacterial and viral infections among adults in an emergency room. Other groups have since replicated that finding, found ways to perform the test more quickly and easily, and demonstrated that it works in children. Performing the test on babies in a hospital setting is a significant advance, says Malergue. It was crucial to investigate the test in this age group because their immune systems are still developing, which meant some people had doubts about the capacity of these markers to arise, he says.
Malergue also notes that one of his collaborators used the test in Martinique during an outbreak of dengue fever, which is caused by a virus and is usually mild. The collaborator found that some people actually had a bacterial infection called leptospirosis, which is life-threatening without antibiotics. This highlights the test's potential to catch dangerous bacterial infections that might otherwise be missed.
Bellini now hopes to assess the test in a trial of 300 to 500 infants at multiple hospitals. Meanwhile, Malergue and his colleagues have developed a benchtop machine that can quickly analyse finger-prick blood samples to determine whether an infection is viral or bacterial. The machine is approved for research use. If the test proves successful in larger trials, it could become a valuable tool for paediatric emergency care, helping doctors make faster, more accurate decisions and reducing the unnecessary use of antibiotics in vulnerable infants.