The Same-Day Test That 'Saved Her Life': Rapid Infection Diagnosis Is Changing Care for Children

"The fact that they had a test there available to her was paramount. It saved her life." Stacey Moore is describing the moment doctors at Great Ormond Street Hospital in London deployed a pioneering same-day test on her 10-year-old daughter Willow — a test that found a hidden, drug-resistant infection everyone else had missed, and put the critically ill child on the treatment that would save her. Willow's story, published alongside new research in The Lancet Microbe, is the human face of a diagnostic breakthrough that doctors say could transform intensive care for children.

The test, known as metagenomic sequencing, scans every scrap of genetic material in a single patient sample — hunting bacteria, viruses and fungi simultaneously instead of asking doctors to guess which germ to look for first. In a study of 122 critically ill children, it detected around nine in ten bacteria and viruses and every fungus present, found 50 organisms that routine tests had missed entirely, and changed the treatment in about a quarter of cases. It is, researchers say, the biggest advance in infection diagnosis in decades.

Willow's fight for life

Willow Crowther, from Kent, was already familiar with hospitals. The 10-year-old has Kabuki syndrome, a rare genetic disorder that affects multiple body systems — causing characteristic facial features, developmental delays and growth abnormalities — and she also lives with epilepsy. But nothing prepared her family for March 2026, when a prolonged seizure led to her hospitalisation and then to the unthinkable: her heart stopped, not once but repeatedly, in a series of cardiac arrests that left her clinging to life.

Her mother was told Willow had an even chance of surviving — a coin toss. She was intubated and transferred to Great Ormond Street Hospital, where she was still critically ill and continued to suffer cardiac arrests. Moved to the hospital's specialist cardiac intensive care unit, she was placed on ECMO, a form of life support that takes over the work of the heart and lungs while doctors fight to find and treat the underlying cause. "She is a sassy 10-year-old who loves the trampoline and Harry Styles," her mother Stacey, 40, a semi-permanent make-up specialist, said later. "It was heartbreaking to see her so ill."

The underlying culprit was pneumonia — but a pneumonia that was not behaving as expected. Willow had been given an antibiotic, yet she was not improving, and nobody could say precisely why. That is where the new test came in.

The test that looks for everything

Metagenomic testing works on a radically different principle from the diagnostics doctors have relied on for generations. The standard method for identifying a bacterial infection is to try to grow the bacteria in a Petri dish — a technique that dates back to Victorian times. It works only for organisms that can be coaxed to grow in a laboratory, it takes days, and it fails entirely for many important pathogens. The other common tool, PCR, is faster but blinkered: it can find viruses and some bacteria only when doctors specify in advance exactly what they are trying to detect.

Metagenomics removes the guesswork. A respiratory sample — in Willow's case, blood was also tested for unknown organisms — is sequenced in full, and the resulting genetic data is compared against libraries containing thousands of known pathogens. Bacteria, viruses and fungi are all hunted at once, from a single sample, with results available the same day. Crucially, the test can also reveal drug-resistance genes, telling doctors not just which germ is present but which medicines will fail against it.

For Willow, that distinction was everything. The testing identified Mycoplasma pneumoniae — a bacterium that is impossible to grow through standard laboratory processes and can only be confirmed by PCR if doctors think to look for it. Even then, standard PCR could never have revealed what the metagenomic test showed: that this particular strain was resistant to the antibiotic she had already been prescribed. Switched to the right treatment, Willow began to recover — though she still needed several months in hospital before she could go home. "It's a miracle she's here and we're extremely grateful for that," her father Russ said.

The numbers behind the breakthrough

Willow was one of 122 children in Great Ormond Street's paediatric intensive care unit whose respiratory samples were analysed with metagenomic testing during 2024 and 2025. The results, now published in The Lancet Microbe, are striking. The test identified around nine in ten of the bacteria and viruses present in the samples, and every single fungus — a class of pathogen that conventional testing routinely misses.

Perhaps most significantly, the service detected 50 organisms that had not been identified by routine diagnostic tests at all, with every one subsequently confirmed by additional testing. In about a quarter of cases, the results directly influenced prescribing decisions — starting, stopping or changing an antibiotic. For children in intensive care, where hours matter and the wrong antibiotic can be as dangerous as none, that is a profound shift.

The study represents the world's first same-day metagenomics service for children, and its architects are clear about what it replaces: an era in which the sickest children were treated on the basis of educated hunches. As Dr Sam Ray, consultant in paediatric intensive care medicine at Great Ormond Street and a co-author of the study, put it, traditional testing required clinicians to make an educated guess about which infection they were looking for — and guesses, however educated, miss things.

From guesswork to precision — and the fight against superbugs

The implications reach far beyond any single hospital. One of the test's most important effects is subtractive: it tells doctors when to stop. "Removing unnecessary treatment is incredibly important for the fight against growing antimicrobial resistance," Dr Ray said. Antibiotics given "just in case" — the default in intensive care, where uncertainty can kill — drive the evolution of drug-resistant superbugs. A test that can confidently rule infections in or out within hours lets clinicians de-escalate treatment rather than piling on ever-broader drugs.

That matters because antimicrobial resistance is one of the great slow-burning crises in global health, estimated to contribute to millions of deaths each year. Paediatric intensive care units are on its front line: the children there are uniquely vulnerable, their immune systems immature or compromised, and the infections they face are increasingly resistant to first-line drugs. Willow's drug-resistant Mycoplasma is exactly the kind of case that would once have been treated blindly — and lost.

There is also a subtler benefit. Because metagenomics sequences everything in a sample rather than hunting a named suspect, it can spot organisms nobody was looking for — including emerging or unusual pathogens. Researchers say the approach could play an early-warning role against new infections, flagging the unfamiliar before it spreads. In a world still absorbing the lessons of the Covid-19 pandemic, a hospital test that doubles as a surveillance system is a tantalising prospect.

What comes next: from one hospital to thirty

The Great Ormond Street service is no longer an experiment. Following the study's results, the same-day metagenomic testing is being rolled out to thirty intensive care units across the United Kingdom — a scale-up that will test whether the benefits seen in one world-leading children's hospital can be reproduced in ordinary NHS settings, with ordinary staffing and ordinary budgets.

Challenges remain. Sequencing is still more expensive than a Petri dish, the data analysis requires specialist expertise, and the test missed around one in ten infections in the study — a reminder that no diagnostic is perfect, and that clinical judgement is not about to be automated away. Questions of equity loom too: the children who would benefit most are often in the hospitals least able to afford cutting-edge genomics.

But for families like the Crowthers, the argument is already settled. Willow went home after months in hospital; her parents describe a miracle, and credit a test. "The fact that they had a test there available to her was paramount," her mother said. Behind that simple sentence lies a quiet revolution in how medicine finds the infections it cannot see — and, increasingly, how it cures the children it once could only guess at.

FAQs

What exactly is metagenomic testing?
It is a diagnostic technique that sequences all the genetic material in a patient sample at once, then matches the sequences against databases of thousands of known pathogens. Unlike conventional tests, it does not require doctors to decide in advance which germ to look for — it can detect bacteria, viruses and fungi simultaneously, and can also identify genes that make infections resistant to particular antibiotics.

How is it different from a normal infection test?
The traditional method grows bacteria in Petri dishes, a Victorian-era technique that takes days and fails for organisms that will not grow in a lab. PCR testing is faster but only finds what doctors specifically ask it to find. Metagenomics needs no prior hypothesis, returns results the same day, and in the Great Ormond Street study found 50 organisms that routine testing had missed entirely.

Will this test be available in every hospital?
Not yet. It began as a world-first service at Great Ormond Street Hospital and is now being rolled out to thirty intensive care units across the UK. Wider availability will depend on costs falling, on training staff to interpret complex sequencing data, and on health systems deciding the investment is justified. For now it is concentrated in intensive care, where the sickest patients — and the greatest diagnostic uncertainty — are found.

What is Kabuki syndrome, the condition Willow lives with?
Kabuki syndrome is a rare genetic disorder affecting multiple body systems. It causes characteristic facial features, developmental delays, growth abnormalities and, in many cases, immune or neurological complications such as the epilepsy Willow experiences. Children with rare genetic conditions are often frequent hospital patients, which is why her family knew Great Ormond Street so well when she became critically ill.

Can metagenomic testing help adults too?
In principle, yes — the technology is not age-specific, and similar approaches are being explored in adult intensive care, transplant medicine and the investigation of unexplained fevers. The Great Ormond Street study focused on children because paediatric intensive care faces particular diagnostic challenges, but researchers expect the technique to spread across medicine as costs fall and the evidence base grows.