The retrospective study reviewed four consecutive children aged between 13 and 26 months who were admitted to Vietnam National Children’s Hospital between June and December 2022. To be included, each child had to show acute neurological dysfunction together with adenovirus detected by real-time polymerase chain reaction, or PCR, in both the cerebrospinal fluid and a nasopharyngeal specimen. This dual requirement is important: it demonstrates that the virus was circulating systemically and that viral DNA had also reached the compartment surrounding the brain and spinal cord. All four children were previously healthy, with no known immunodeficiency that would predispose them to overwhelming viral infection, which makes the severity of their presentations all the more unusual and clinically significant.

The cerebrospinal fluid findings are the technical heart of the paper. In classical viral encephalitis or meningitis, clinicians expect a pleocytosis, an elevated number of white blood cells in the spinal fluid, typically accompanied by raised protein. In these four toddlers, leukocyte counts ranged from just 1 to 3 cells per microliter, values that would generally be considered within or barely above the normal range, and protein concentrations ranged from 0.38 to 0.62 grams per liter, likewise unremarkable. Yet real-time PCR returned positive results for adenovirus in every sample. The authors argue that such near-normal indices do not exclude clinically important adenovirus-associated central nervous system disease, and that clinicians should not be falsely reassured by a clean-looking spinal tap when a child is neurologically deteriorating in the context of systemic adenoviral illness.

Neuroimaging added further complexity. Brain magnetic resonance imaging was performed in two of the four children. One scan showed bilateral frontoparietal cortical lesions compatible with encephalitic involvement, providing objective evidence that the brain parenchyma itself was affected. The other showed nonspecific widening of the frontoparietal subarachnoid spaces, a finding that could reflect cerebral volume loss or atrophy but is not diagnostic of any single process. The limited imaging data reflect the realities of retrospective case series in an intensive care setting, where the sickest children may be too unstable for transport to the scanner. Even so, the images underscore that adenovirus can produce structural brain injury in immunocompetent toddlers, not merely self-limited meningitic symptoms.

The systemic component of the illness was equally severe. All four children required invasive mechanical ventilation, and one additionally needed extracorporeal membrane oxygenation, a heart-lung bypass technique reserved for patients whose respiratory or circulatory failure cannot be managed by a ventilator alone, as well as renal replacement therapy for kidney failure. The combination of respiratory failure, circulatory collapse, renal injury, and neurological dysfunction in previously healthy toddlers illustrates the fulminant, multisystem character of the syndrome. Adenovirus is capable of infecting respiratory epithelium, gastrointestinal tract, liver, and other organs, and in these cases the infection appears to have triggered a cascade of organ dysfunction that outpaced the children’s physiological reserves.

A particularly notable laboratory feature was marked hyperferritinemia, an extremely elevated blood level of ferritin, the iron-storage protein. Very high ferritin values are a hallmark of systemic hyperinflammation and are seen in conditions such as macrophage activation syndrome and hemophagocytic lymphohistiocytosis, disorders in which the immune system’s scavenger cells become pathologically activated and release a storm of inflammatory cytokines. In this series, two children received a clinical diagnosis of macrophage activation syndrome during their admission, although the authors note that a complete evaluation according to the HLH-2004 criteria was not performed. This raises the possibility that at least part of the tissue damage in these children was driven not by direct viral cytopathic effect but by a runaway inflammatory response to the infection, a mechanism with important implications for treatment.

The therapeutic implications are considerable. If hyperinflammation contributes substantially to the deterioration of these patients, then immunomodulatory strategies, such as those used in macrophage activation syndrome or hemophagocytic lymphohistiocytosis, might theoretically be considered alongside antiviral therapy and organ support. At the same time, the authors are careful to draw a boundary around what their data can support. They conclude that escalation of respiratory, circulatory, renal, or extracorporeal support should be guided by the child’s physiological deterioration and objective measures of organ dysfunction, rather than by cerebrospinal fluid PCR positivity alone. In other words, finding adenoviral DNA in the spinal fluid is a diagnostic clue, not a treatment algorithm, and clinical judgment anchored in the patient’s trajectory remains paramount.

Why adenovirus reached the central nervous system in these children, and why the spinal fluid showed so little inflammation, remains unresolved. Several mechanisms are plausible: direct viral invasion of neural tissue, infection of the meninges, or a post-infectious inflammatory process. The paucity of pleocytosis could reflect very early sampling in the disease course, before the inflammatory cascade had spilled into the cerebrospinal fluid, or a pattern of parenchymal rather than meningeal involvement. It is also possible that the profound systemic hyperinflammation altered the usual immunology of the central nervous system compartment. The authors of the series do not claim to have settled these questions; their contribution is to document that the dissociation between positive PCR results and normal routine indices can occur, and that it matters for clinical practice.

The study’s design imposes limits that readers should keep in view. It is a retrospective case series of four children at a single hospital over a six-month period, without a comparison group, and the authors did not perform a complete HLH-2004 workup, so the diagnoses of macrophage activation syndrome rest on clinical assessment. Case series cannot establish incidence, cannot prove causation between adenovirus and the neurological syndrome, and cannot determine whether the outcomes would have differed under alternative management strategies. Nevertheless, the consistency of the pattern, four previously healthy toddlers, all with dual respiratory and cerebrospinal fluid PCR positivity, all requiring mechanical ventilation, and three deaths, is difficult to dismiss as coincidence, and the ethical review board of Vietnam National Children’s Hospital approved the study under the Declaration of Helsinki with consent requirements waived for its retrospective design.

For clinicians caring for young children, the practical message is one of heightened vigilance rather than alarm. Adenovirus remains a common and usually benign pathogen of early childhood. But when a toddler with confirmed or suspected adenoviral infection develops new neurological dysfunction, whether seizures, altered consciousness, or focal signs, the new data suggest that cerebrospinal fluid PCR testing for adenovirus deserves a place in the etiological assessment, even when cell counts and protein are normal or nearly so. Equally, the presence of marked hyperferritinemia and other signs of systemic hyperinflammation should prompt consideration of macrophage activation syndrome in the differential diagnosis. As molecular diagnostics become faster and more widely available, the challenge will be to integrate these sensitive tools with sound physiological reasoning, so that detection of viral genetic material informs, rather than dictates, the care of the sickest children.

Subject of Research: Severe multisystem adenovirus infection with central nervous system involvement in immunocompetent toddlers

Article Title: Fulminant multisystem adenovirus-associated illness with cerebrospinal fluid PCR positivity and minimal pleocytosis in previously healthy toddlers: a case series

Article References: Do, T. H., Van, A. V., Trong, H. D., Thi, H. T. N., & Nguyen, S. D. (2026). Fulminant multisystem adenovirus-associated illness with cerebrospinal fluid PCR positivity and minimal pleocytosis in previously healthy toddlers: a case series. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07691-9

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07691-9

Keywords: adenovirus, cerebrospinal fluid, PCR, encephalitis, hyperinflammation, macrophage activation syndrome, pediatric critical care, toddlers, central nervous system, mechanical ventilation, ECMO, BMC Pediatrics

The study, published in BMC Infectious Diseases, was led by Yalin Sun and colleagues in the hospital’s Department of Pediatric Infectious Diseases. The team examined children aged eighteen years or younger who were hospitalized with acute respiratory tract infections between 5 January 2023 and 17 June 2025. Each child underwent a thirteen-target pharyngeal-swab assay covering the common respiratory pathogens, from respiratory syncytial virus and influenza to human adenovirus and Mycoplasma pneumoniae. The researchers collapsed these detections into eleven analytical groups and then asked a deceptively simple question: did the identity of the detected pathogen predict the child’s inflammatory biomarker levels or the length of their hospital stay?

The scale of the dataset lends the findings considerable weight. Of 6,093 hospitalized children included in the analysis, 2,076 tested negative on the respiratory panel, 3,343 had a single pathogen detected, and 674 carried detections of multiple targets simultaneously. Rather than treating every pathogen individually, the investigators defined three primary outcomes that map onto everyday clinical decisions: a high-sensitivity C-reactive protein value of at least 20 milligrams per liter, a procalcitonin value of at least 0.5 nanograms per milliliter, and a hospital stay lasting seven days or longer. These thresholds are commonly used at the bedside as rough markers of a bacterial process or a complicated course.

The statistical approach was deliberately conservative. Complete-case logistic regression models adjusted for age group, sex, testing year, and season, and the authors applied false discovery rate corrections to guard against spurious associations arising from the many comparisons inherent in a multi-pathogen panel. Sensitivity analyses probed the robustness of the results from several angles: biomarkers were also modeled as continuous variables, multiple-target detections were examined separately, recorded SARS-CoV-2 positivity was accounted for, and the analysis was restricted to children sampled within 24 or 48 hours of admission using both source records and chart-reviewed timing intervals.

Two pathogens stood out with sharply contrasting signatures. Human adenovirus detection was associated with roughly double the odds of an elevated inflammatory response compared with children whose panels came back negative. The adjusted odds ratio was 2.19 for a high-sensitivity C-reactive protein value of at least 20 milligrams per liter, with a 95 percent confidence interval of 1.63 to 2.96, and 1.93 for a procalcitonin value of at least 0.5 nanograms per milliliter, with a confidence interval of 1.34 to 2.77. In practical terms, a child whose swab revealed adenovirus was markedly more likely to show the kind of inflammatory surge that clinicians often associate with bacterial infection, even though adenovirus is a virus.

Mycoplasma pneumoniae told the opposite story in one respect and a striking one in another. Detection of this atypical bacterium was linked to lower odds of a procalcitonin value reaching 0.5 nanograms per milliliter, with an adjusted odds ratio of just 0.22 and a confidence interval of 0.13 to 0.37. Yet the same pathogen was the strongest predictor of a prolonged hospitalization in the entire study: children with Mycoplasma pneumoniae detections had 2.57 times the odds of staying seven days or longer, with a confidence interval of 1.99 to 3.31. The association with long stays persisted when the analysis was restricted to children sampled early, yielding adjusted odds ratios of 2.50 in the 24-hour subset and 2.76 in the 48-hour subset, suggesting that the finding was not an artifact of delayed testing after several days of illness.

Multiple detections carried their own signal. Children in whom two or more targets were identified had 2.21 times the odds of a hospital stay of at least seven days compared with panel-negative children, with a confidence interval of 1.73 to 2.82. Co-detection is increasingly recognized as common rather than exceptional in pediatric respiratory medicine, and this result adds to the evidence that a positive panel with more than one organism is not simply noise. Whether co-detected pathogens interact biologically, or whether multiple detections mark a different underlying illness severity, remains an open question that this observational design cannot resolve.

The authors are careful, and rightly so, about what these numbers do and do not mean. A retrospective cohort of routine clinical data cannot establish that a pathogen causes a longer stay or a higher biomarker value. Unmeasured bacterial infection, variation in treatment, differences in illness severity at presentation, and the clinical selection of which children get tested all could shape the observed associations. The study also relied on routinely recorded biomarkers rather than protocol-mandated sampling, and chest radiograph findings were classified from reports in a way the authors flag as unvalidated. These limitations are acknowledged explicitly in the paper, and the sensitivity analyses, while reassuring, do not convert association into causation.

Even with those caveats, the clinical implications are worth pondering. The adenovirus finding serves as a caution against over-relying on C-reactive protein and procalcitonin as bacterial discriminators: a vigorous inflammatory response in a child with a positive adenovirus swab may reflect the virus itself rather than a bacterial co-infection demanding antibiotics. Conversely, the Mycoplasma pneumoniae result suggests that a low procalcitonin does not guarantee a short or uncomplicated course. Mycoplasma infections in children are notorious for protracted coughing illness and, in some regions, rising macrolide resistance, and a biomarker pattern that looks reassuringly quiet may coexist with a hospitalization that stretches well past a week.

For researchers, the study illustrates the value of linking routine diagnostic panels to outcomes data at scale, and of stress-testing associations with early-sampling restrictions and timing reconciliation before publication. The supplementary materials document an unusually thorough audit trail, including chart-reviewed corrections of PCR timing records and analyses omitting individually corrected entries. For clinicians, the takeaway is more modest but useful: pathogen identity, inflammatory biomarkers, and hospital course each carry independent information, and none substitutes for the others. As multiplex panels become faster and cheaper, studies like this one help map which detections actually matter for the questions that keep a child in the hospital, and which are simply molecular footnotes to an illness that will resolve on its own schedule.

Subject of Research: Associations between multiplex respiratory pathogen detections, inflammatory biomarkers, and length of stay in children hospitalized with acute respiratory tract infections

Article Title: Respiratory panel detections, inflammatory biomarkers, and length of stay in children hospitalized with acute respiratory tract infections: a retrospective cohort study

Article References: Sun, Y., Li, S., Wang, Y., Zhang, S., Teng, S., & Qi, Z. (2026). Respiratory panel detections, inflammatory biomarkers, and length of stay in children hospitalized with acute respiratory tract infections: a retrospective cohort study. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14559-x

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14559-x

Keywords: acute respiratory tract infection, children, multiplex PCR, human adenovirus, Mycoplasma pneumoniae, procalcitonin, C-reactive protein, length of stay, biomarkers, pediatrics, retrospective cohort, hospitalization

The research, led by Mustafa Karatas and Jelle Matthijnssens of the Laboratory of Clinical and Epidemiological Virology at KU Leuven, applied hybrid-capture viral metagenomics to 127 weekly 24-hour composite influent samples collected from a single sentinel wastewater treatment plant in Leuven, Belgium, over a span of 31 months. Rather than amplifying a predefined genetic target, the team used panels of synthetic probes designed to bind viral genetic material across a broad range of virus families. These probes capture fragments from the complex wastewater mixture, enriching them relative to the overwhelming background of bacterial, fungal, plant and human DNA and RNA, and thereby allowing deep sequencing to recover near-complete viral genomes from the sample.

The technical payoff was substantial. Across the 31-month monitoring window, the approach recovered a genome-resolved, target-enriched virome spanning 339 viral species and 715 distinct strains. This depth of resolution matters because public health decisions increasingly depend on knowing not just whether a virus is present, but which variant or genotype is circulating. For RNA viruses with high mutation rates, such as SARS-CoV-2 or norovirus, strain-level identification can signal the arrival of a new variant with altered transmissibility or immune escape properties long before clinical laboratories compile comparable data.

To validate the biological meaning of the wastewater signals, the researchers linked their time series to national clinical surveillance indicators for multiple pathogens. The concordance analysis showed that wastewater and clinical data tracked each other closely for several medically important viruses, including rotavirus A, SARS-CoV-2 and human mastadenovirus. For rotavirus A, a leading cause of severe childhood gastroenteritis, viral genetic material in sewage typically preceded clinical surveillance signals by approximately one week. That lead time, consistent with theoretical models of wastewater-based epidemiology, reflects the interval between infection, shedding of virus into sewage, and the delay before symptomatic patients seek care and are formally tested and reported.

Beyond confirming known pathogens, the longitudinal design revealed signals that routine surveillance programmes missed entirely. The most striking example was a surge of parvovirus B19 beginning in April 2023, roughly one year before the national public health alert was issued in Belgium. Parvovirus B19, which causes fifth disease in children and can produce severe complications in pregnant people and immunocompromised patients, is not part of standard wastewater monitoring panels. Its detection in the Leuven sewage time series illustrates the core advantage of a broad hybrid-capture approach: because the probe panel targets many virus families at once, the method can flag unusual increases in pathogens that no one thought to monitor, without requiring a new assay to be designed and deployed.

The strain-resolved dimension of the study also extended to rotavirus genotyping. Rotavirus A carries a segmented double-stranded RNA genome, and its genotype constellation, defined by the combination of G-type and P-type segments, can shift through reassortment and interspecies transmission. The wastewater data captured the temporal dynamics of rotavirus genotypes and identified unusual genotype constellations circulating in the community, including equine-like G3P[8] strains whose post-pandemic dominance in Belgium had previously been documented through clinical sampling. Recovering this information from sewage, without culturing or clinical specimen collection, shows that hybrid-capture metagenomics can serve as a genuine molecular epidemiology tool rather than a mere presence-absence detector.

Seasonal community turnover was another feature the multi-year dataset made visible. The viral composition of wastewater shifted predictably with the seasons, with enteric viruses peaking in winter months and respiratory viruses following their own epidemic rhythms. Because the samples were collected weekly from the same treatment plant serving a stable population, the researchers could distinguish genuine epidemiological trends from sampling noise, and the principal-coordinate analysis of viral community composition revealed coherent clustering by season and epidemic phase. This longitudinal perspective is precisely what episodic studies, which sample during outbreaks and stop afterwards, cannot provide.

The study also addresses a practical question facing surveillance programmes worldwide: what happens to wastewater monitoring after the COVID-19 emergency? Many programmes built during the pandemic have struggled to justify continued funding for single-pathogen assays. The Leuven results suggest an answer in the form of economies of scope. A single hybrid-capture workflow, applied consistently, generates data on hundreds of viruses at once, including SARS-CoV-2 variants, noroviruses, enteroviruses, adenoviruses, astroviruses and rotaviruses, along with less expected agents such as parvovirus B19. The marginal cost of watching an additional pathogen within the same pipeline is far lower than launching a separate targeted programme for each new threat, a consideration that becomes critical when novel viruses such as avian influenza H5N1 raise concerns about zoonotic spillover.

The researchers have made their analytical resources available to the community, including curated rotavirus A genotyping databases and scripts to reproduce the figures, hosted on GitHub, and the raw sequencing data, with human-associated reads removed for privacy, deposited in the Sequence Read Archive under accession PRJNA1391037. This openness lowers the barrier for other laboratories to adopt the approach and benchmark their own sentinel sites against the Leuven time series.

Limitations remain, as the authors and commentators in the field acknowledge. Hybrid-capture enrichment depends on probe design, so truly novel viruses divergent from panel targets may evade capture, and quantitative interpretation of wastewater read counts requires careful normalization against population size, shedding rates and sewer hydrology. Nonetheless, the study establishes a benchmark for what longitudinal, multi-pathogen, strain-resolved wastewater surveillance can achieve. By demonstrating a full year of early warning for parvovirus B19, a consistent one-week lead over clinical reporting for rotavirus A, and genome-resolved tracking of 715 viral strains from a single treatment plant, the work makes a compelling case that the future of wastewater-based epidemiology lies not in narrower tests, but in broader, deeper and longer views of the viruses circulating silently through urban populations.

Subject of Research: Hybrid-capture metagenomic sequencing of wastewater for longitudinal, strain-resolved surveillance of human-associated viruses

Article Title: Hybrid-capture-enabled longitudinal metagenomics allows strain-resolved human-associated virus surveillance in wastewater

Article References: Karatas, M., Bloemen, M., Swinnen, J., Close, L., Van Ranst, M., Wollants, E., & Matthijnssens, J. (2026). Hybrid-capture-enabled longitudinal metagenomics allows strain-resolved human-associated virus surveillance in wastewater. Nature Water, 4(9), 1128-1138. https://doi.org/10.1038/s44221-026-00693-y

Image Credits: AI Generated

DOI: 10.1038/s44221-026-00693-y

Keywords: wastewater surveillance, hybrid capture, viral metagenomics, strain-resolved, rotavirus A, SARS-CoV-2, parvovirus B19, adenovirus, public health, epidemiology, KU Leuven, Nature Water