Blood test could gauge if a baby has a dangerous infection in 15 minutes

Blood tests can reveal a lot about a baby’s health

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A blood test could determine whether a feverish baby has a bacterial or viral infection in 15 to 20 minutes. This would help doctors gauge whether the infection is serious or may pass without treatment, which could prevent unnecessary use of antibiotics.

When babies are brought into hospital with fever, they “are considered high-risk until proven otherwise”, says Tommaso Bellini at the Giannina Gaslini Institute in Genoa, Italy.

A fever can be the result of several things, including infection by viruses or bacteria. These different types of pathogens require different medications. Furthermore, most common viruses are fairly benign, while bacterial infections are generally more dangerous, says Bellini.

Existing tests to gauge infection type take at least a few hours, so babies with fever are often given antibiotics against bacteria as a precautionary measure. But only about 15 per cent of them actually have a serious bacterial infection, says Bellini. This unnecessary use of antibiotics helps drive the spread of bacterial resistance.

To develop a test that determines infection type, Bellini and his colleagues followed 85 babies, all younger than 90 days old, who were brought into emergency rooms with fever after previously having no 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 made 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 incidences 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, says Bellini, who is trying to develop a version that can be used as quickly in hospitals.

This builds on several years of research 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 [CD64 and CD169] markers to arise”, he says.

Malergue says 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.

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, which is approved for research use.