Adult Invasive Enterovirus Detection Was Concentrated in Cerebrospinal Fluid
Adult invasive infections caused by enterovirus and parechovirus were identified across Alberta over three years, and the laboratory pattern was strikingly centered in cerebrospinal fluid. Among 15,621 specimens received for testing from 2023 through 2025, 162 were positive for virus, representing 1.0% of all samples. Of those positive viral detections, 51 met criteria for invasive infection, or 31.5% of positive specimens. The remaining positive detections were noninvasive or came from sites outside the invasive infection definition used in the study.
The yearly volume of specimens grew steadily, from 3,723 in 2023 to 5,767 in 2024 and 6,131 in 2025. Viral positivity stayed almost unchanged at 1.1%, 1.0%, and 1.0% across those years. The invasive subset, however, fluctuated: 15 invasive infections in 2023, 9 in 2024, and 27 in 2025. The rise in 2025 is difficult to interpret from the table alone, but the numbers suggest a sharper burden of clinically meaningful disease in that year, even as the overall positivity rate remained stable.
One specimen source dominated the invasive cases. Cerebrospinal fluid accounted for 40 of 51 invasive infections, or 78.4%. Blood contributed 8 cases, and sterile tissue samples accounted for 3. The distribution matters because invasive enterovirus disease in adults often travels through the central nervous system or bloodstream before it is recognized clinically. In that setting, CSF positivity is not merely a laboratory detail; it is the anchor that often distinguishes true invasive disease from incidental viral detection at nonsterile sites.
The Laboratory Pattern Fits Central Nervous System Involvement
The CSF-heavy pattern is consistent with the biology of these pathogens. Enteroviruses and parechoviruses can invade sterile compartments when viremia seeds the central nervous system or other protected tissues. Adult invasive infection is less commonly discussed than pediatric disease, yet the specimen profile here shows that adults can present with syndromes severe enough to prompt sterile-site sampling. The fact that 78.4% of invasive detections came from CSF suggests neurologic presentations or concern for meningitis-like illness were a major driver of testing, even though the table does not provide symptom data.
A single number gives the clearest bedside signal: 40 invasive infections were detected in CSF, while only 8 were found in blood.
This difference is clinically important because it implies that routine blood testing alone would have missed much of the invasive burden. In practice, that can delay recognition in adults whose illness appears nonspecific at first or whose neurologic symptoms evolve after an initial febrile phase. The microbiologic yield from CSF also reinforces why lumbar puncture remains central when clinicians suspect invasive enteroviral disease. Without a sterile-site sample, the diagnosis can remain hidden.
Year-to-Year Shifts Suggest a Changing Adult Burden
The total number of positive viral specimens rose from 42 in 2023 to 58 in 2024 and 62 in 2025, while the proportion of all received specimens that were virus-positive remained constant at about 1.0%. That stability implies the testing volume expanded more quickly than the positivity rate. The invasive subset did not follow a linear pattern, which is exactly the sort of signal surveillance tables can reveal before the underlying drivers are fully understood.
In 2023, every invasive detection came from CSF. In 2024, the pattern broadened modestly, with 8 CSF samples and 1 blood sample. By 2025, the distribution was more mixed: 17 CSF samples, 7 blood samples, and 3 sterile tissue samples. The appearance of sterile tissue detections in 2025 may reflect broader specimen collection practices, a change in clinical suspicion, or a real shift in disease expression. The table does not allow a definitive explanation, but it does show that invasive adult infection was not confined to one specimen type by the end of the surveillance period.
What the Numbers Do and Do Not Prove
This table is concise, and its narrow scope imposes real limits. It does not provide age bands, sex distribution, comorbidities, presenting syndromes, viral subtypes, outcomes, or whether the same patient contributed more than one specimen. It also does not show the absolute number of patients tested, only the number of specimens received. Because some patients contributed multiple samples, specimen counts cannot be equated with case counts.
Even so, the dataset is clinically useful. It documents that invasive adult enterovirus and parechovirus infections were repeatedly detected over three consecutive years in a provincial laboratory system, with a clear predominance of CSF positivity. That pattern should keep these pathogens on the differential diagnosis in adults evaluated for aseptic meningitis, unexplained neurologic illness, or other invasive syndromes that prompt sterile-site sampling. The laboratory signal is small in absolute percentage terms, but invasive disease was a meaningful fraction of positive viral detections and not a rare one-off event.
From a public health perspective, the numbers also argue for sustained diagnostic awareness rather than opportunistic testing alone. When adult invasive enteroviral disease is only recognized after CSF is sent, the burden can be underestimated. Surveillance based on sterile-site testing is more likely to capture the severe end of the spectrum, which is exactly where clinical and infection-control decisions tend to hinge.
The table leaves the most important causal questions unresolved: whether the 2025 increase reflects a true rise in incidence, altered testing patterns, or both. It also does not clarify how often blood or tissue sampling added diagnostic value beyond CSF. Those unanswered points matter because they determine how laboratories and clinicians should prioritize specimen collection when adult invasive infection is suspected.