Same-day metagenomic testing changes the pace of infection diagnosis in paediatric ICU
A single respiratory sample can now reveal more than clinicians were able to see with standard testing, and in critically ill children that speed can alter the course of treatment within hours. At Great Ormond Street Hospital, a same-day metagenomic test was used in more than 100 children in intensive care, identifying hidden and drug-resistant infections that conventional methods missed. In a setting where pneumonia, sepsis, and multi-organ instability can deteriorate rapidly, the difference between guessing and knowing is clinically decisive.
One child’s case made that difference painfully concrete. Ten-year-old Willow Crowther became dangerously ill with pneumonia in March after a seizure and multiple cardiac arrests, then required admission to intensive care. Her mother was told survival was uncertain. The new test identified a drug-resistant bacterial infection and pointed doctors toward a different antibiotic than the one she had first received. Her recovery took months, but the diagnostic result redirected care when the margin for error was vanishingly small.
The biology behind the test explains why it carries such force in intensive care. Instead of asking a laboratory to look only for a specific suspected organism, metagenomics sequences all genetic material present in the sample. That approach can detect bacteria, viruses, and fungi in one pass, including pathogens that routine culture or targeted PCR may miss. In a child already deteriorating on broad-spectrum treatment, the ability to identify the organism without first making an educated guess can shorten the path to an effective drug and reduce exposure to antibiotics that will not work.
What the GOSH cohort found in critically ill children
During the 2024–25 study period, metagenomic testing was applied to 122 critically ill children in the paediatric intensive care unit at GOSH. Results published in The Lancet Microbe showed the test could identify around nine in 10 bacteria and viruses, and all fungi present in samples. In one quarter of cases, the result changed prescribing decisions, including starting, stopping, or switching an antibiotic. Those are not abstract laboratory wins; they are bedside decisions that determine whether a child receives coverage that is too narrow, too broad, or simply wrong.
The study also identified 50 organisms not found by routine diagnostics. Some of those findings matter because they represent infections that standard pathways would have overlooked altogether. Others matter because they may help clinicians interpret persistent fever, respiratory decline, or a failure to improve despite conventional therapy. In paediatric intensive care, where time pressure forces clinicians to treat before every answer is available, an assay that broadens detection without losing speed changes the diagnostic frame.
Traditional methods still dominate routine practice. Culture remains the long-standing standard for bacterial identification, yet it depends on the organism growing in a Petri dish and often takes time that the sickest children do not have. PCR is faster, but it requires clinicians to define the target in advance. Metagenomics removes that prior constraint. It does not replace clinical judgement; it extends it by exposing the infectious possibilities hidden inside a single sample.
A short result window can also change antibiotic stewardship in the opposite direction. When the test shows that no relevant pathogen is being found, treatment can be stopped rather than prolonged by inertia. That matters in a hospital environment where antimicrobial resistance is no longer a distant policy problem but a daily clinical constraint. Every unnecessary course of antibiotics exerts selection pressure. Every missed resistant organism delays effective treatment.
Why drug resistance and missed pathogens matter at the bedside
Dr Sam Ray, consultant in paediatric intensive care medicine at GOSH and co-author of the study, described the central problem plainly: conventional testing asks clinicians to make an educated guess about what they are looking for. In critically ill children, those guesses often lead to empiric treatment before the true pathogen is known. A metagenomic result can tighten that uncertainty quickly, revealing infections that would otherwise remain hidden and allowing antibiotics to be refined rather than continued by default.
The same principle applies to fungi and emerging pathogens. Metagenomics at GOSH was able to detect all fungi in samples, a meaningful advantage in children whose immune systems may be compromised or whose clinical picture is too complex for a narrow test panel. Dr Julianne Brown, head of the GOSH Metagenomics Service and co-senior author of the study, said the service is being rolled out gradually to around 30 intensive care units across the UK treating adults and children. The broader significance is not confined to routine ICU care. A platform that can surface unfamiliar organisms quickly could serve as an early warning system if a new pathogen begins to circulate.
That surveillance potential is one of the most important clinical implications of the work. If a mystery pathogen were to appear, a diagnostic system built to read all genetic material in a specimen would not need the same degree of prior suspicion. In practice, that means a lab may be able to flag an unusual infectious signal earlier than a conventional targeted approach. In a future outbreak, that kind of capability could shape isolation decisions, antimicrobial choices, and the speed with which infection-control measures are put in place.
The GOSH project also builds on earlier work at Guy’s and St Thomas’ NHS Trust, where metagenomics was first used to test for respiratory infections in adult patients. The paediatric ICU data add a different layer: smaller patients, narrower physiological reserve, and a higher premium on every hour saved. Even when the final treatment remains familiar, the route to reaching it becomes more precise.
For Willow and the other children in the cohort, the value of the test was immediate and tangible. It identified infections that routine methods missed, and it sometimes told doctors to abandon treatment that was not going to help. The study leaves open practical questions about how widely the technology can be embedded, how quickly results can be returned in smaller centres, and how best to use it alongside standard microbiology. Those questions now sit next to a more basic one: in the sickest children, how much harm can be avoided when the right pathogen is named before the window for rescue closes.