60 babies, two markers: the blood test that told bacterial fever from viral
What happened
Doctors in Genoa, Italy, have tested a quick blood test that tries to answer one of the hardest questions in children's emergency care: is this baby's fever caused by bacteria, or by a virus? The results were presented on 27 September 2026 at the European Emergency Medicine Congress, the annual meeting of the European Society for Emergency Medicine. The test does not look for the germ itself. Instead it measures two markers found on white blood cells and compares them. One of them is called CD64. It sits on the surface of neutrophils, a type of white blood cell, and levels of it are thought to rise when the body is fighting a bacterial infection. The test turns the two measurements into a single score. The team used it on 60 babies brought to the paediatric emergency department at the IRCCS Istituto Giannina Gaslini in Genoa with a fever. The scores came out very differently depending on what was wrong. Babies with no infection had an average score of 1.10. Babies with a confirmed viral infection averaged 0.33. Babies with a confirmed bacterial infection averaged 16.22. In this group, the test picked up every bacterial infection that was there. Its sensitivity was 100% and its specificity was 96.6% - meaning it very rarely flagged a bacterial infection when there was not one.
Why this matters
A high temperature in a baby under three months old is treated as a medical emergency in the UK and across Europe. That is not scaremongering. Very young babies have immune systems that are still getting going, and an infection that would give an adult a rough week can become life-threatening in a newborn within hours. Because of that, hospitals are deliberately cautious. A feverish newborn often has blood taken, sometimes a lumbar puncture, and is usually started on antibiotics and admitted while the lab results are awaited. That wait can be a day or more. Most of those babies turn out to have a virus. Antibiotics do nothing at all for a virus. So a lot of very small babies are admitted, given drips and given antibiotics they never needed, because at the moment there is no fast, reliable way to tell. The cost of that caution is real: distress for the baby, worry and lost sleep for the family, hospital beds used up, and antibiotics given out unnecessarily at a time when antibiotic resistance is one of the biggest long-term threats to medicine. A test that could sort the two apart quickly would not remove the need for careful doctors. It would give them better information sooner.
What the evidence actually says
It is worth being clear about how much - and how little - this study shows. Sixty babies is a small study. The researchers themselves describe it as relatively small. A 100% sensitivity result in 60 patients is encouraging, but it is not the same as a 100% sensitivity result in 6,000. With small numbers, a single unusual case can move the figures a long way. The study was also done in one hospital, in one city, in one country. Babies arriving at a specialist children's hospital in Genoa may not be the same mix as babies arriving at a district general hospital in Lincolnshire. It was presented at a conference. Conference presentations are how new findings are first shared with other doctors, and they are an important part of how medicine moves forward. But they have usually not yet been through the full peer-review process that a journal paper goes through, where independent experts pick the methods apart. What the study does do is add to a body of work on host-response testing - the idea of measuring how your body is reacting, rather than hunting for the germ. That approach is being studied hard across Europe, precisely because everyone recognises the antibiotic problem. So: a promising early signal, from a real hospital, with real babies. Not a test you can ask for at your GP surgery tomorrow. Larger studies in more hospitals would need to repeat the result before anything changes in routine NHS care.
Practical advice
None of this changes what a parent or carer should do today. The NHS advice stands, and it is deliberately simple. Call 111 if your baby is under 3 months old and has a temperature of 38C or higher - or if you simply think they have a high temperature. You do not need to be sure. You do not need a thermometer reading to justify the call. Trusting your instinct is the advice, not an exception to it. A few practical things that help: Keep a digital thermometer in the house if you have a baby, and check you know how to use it before you need it in the middle of the night. Write down when the temperature started and what it has been. Staff will ask, and it is hard to remember accurately when you are frightened. Look at the whole baby, not just the number. Unusual sleepiness, being difficult to wake, a weak or high-pitched cry, refusing feeds, fewer wet nappies, fast or laboured breathing, or a rash that does not fade when you press a glass against it all need urgent help - call 999 for these, do not wait. If your baby is prescribed antibiotics, finish the course as directed unless a clinician tells you to stop. If you are told your baby has a virus and does not need antibiotics, that is not your doctor fobbing you off. It is the right answer, and it is the answer this new test is trying to reach faster. Do not give aspirin to a child. If you are unsure which medicine, which dose or which age it is for, your pharmacist can check with you before you give it.
What to know
A blood test measuring two white blood cell markers, one of them CD64, separated bacterial from viral infection in 60 feverish babies at a hospital in Genoa. Bacterial cases averaged a score of 16.22, viral cases 0.33, and babies with no infection 1.10. Sensitivity was 100% and specificity 96.6%. It is an early, small, single-hospital study presented at a conference, so it is a promising signal rather than a change to UK care. If it holds up in bigger studies, it could mean fewer newborns admitted and fewer antibiotics given unnecessarily. Until then, the rule for parents has not moved: a temperature of 38C or higher in a baby under three months means calling 111 straight away, and worrying signs mean calling 999. Sources: European Society for Emergency Medicine (EUSEM), 'Press Release: Blood test shows whether newborns with fever have bacterial or viral infection', 27 September 2026, https://www.eusem.org/news/1168-press-release-blood-test-shows-whether-newborns-with-fever-have-bacterial-or-viral-infection; News-Medical, 'Two-molecule blood test accurately identifies infections in febrile infants', 27 September 2026, https://www.news-medical.net/news/20260927/Two-molecule-blood-test-accurately-identifies-infections-in-febrile-infants.aspx; NHS, 'Fever in children', https://www.nhs.uk/conditions/fever-in-children/. This article is for general information and does not replace advice from a doctor, pharmacist or other qualified healthcare professional.
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