Laboratory Studies for Suspected Enterovirus (Rhinovirus) Encephalitis
For suspected enterovirus encephalitis, you should order CSF PCR for enterovirus/parechovirus as the primary diagnostic test, along with throat and rectal swabs (or stool), and respiratory samples if there are concurrent respiratory symptoms. 1
Core Laboratory Testing Algorithm
Cerebrospinal Fluid (CSF) - First Priority
All patients require lumbar puncture with the following studies:
- CSF PCR for enterovirus/parechovirus - This is the single most important test 1
- Opening pressure
- Cell count with differential (total and differential white cell count, red cell count)
- Protein and glucose (compare with simultaneous plasma glucose)
- Gram stain, bacterial culture
- Store additional sample (2 ml) for future testing 1
Critical caveat: Enterovirus PCR on CSF has limitations. Some enteroviruses (particularly EV-D68 and rhinoviruses) are rarely detectable in CSF, making additional sample sites essential 2.
Ancillary Samples - Essential for Enterovirus Detection
Because enteroviruses may not appear in CSF, you must obtain samples from multiple sites 2, 1:
- Throat swab - PCR/culture for enterovirus
- Rectal swab or stool sample - PCR/culture for enterovirus
- Nasopharyngeal aspirate or nasal/throat swab - Particularly important if respiratory symptoms present, as EV-D68 is primarily detected in respiratory specimens 2, 1
Important distinction: Vesicular fluid (if vesicles present) is most useful as it indicates acute systemic infection, whereas fecal carriage can persist long-term and may represent coincidental shedding rather than causative infection 1.
Blood Studies
- Acute serum sample - Store for potential convalescent comparison 1
- Standard admission labs (CBC, comprehensive metabolic panel, coagulation studies if LP planned)
Timing Considerations for Antibody Testing
If initial CSF PCR is negative but enterovirus remains suspected, obtain repeat CSF and serum at 10-14 days post-illness onset for enterovirus-specific IgM and IgG antibody testing 1. Intrathecal antibody synthesis typically appears after 10-14 days and can diagnose cases missed by early PCR 1.
Diagnostic Hierarchy
The 2018 European consensus specifically recommends RT-PCR targeting the 5' noncoding region for diagnosis due to superior sensitivity, specificity, and rapid turnaround compared to viral culture 2. However, the British guidelines note that respiratory and stool samples in addition to CSF are vital because viruses like EV-D68 are rarely detectable in CSF or stool 2.
Common Pitfalls to Avoid
- Don't rely solely on CSF testing - You will miss EV-D68 and some rhinoviruses that don't appear in CSF 2
- Don't interpret positive stool/throat swabs as definitive - These can represent prolonged shedding or carriage unrelated to CNS disease 1
- Don't skip respiratory samples if any respiratory symptoms exist - This is where EV-D68 is primarily found 2
- Don't forget to send HSV, VZV PCR on all CSF samples - These remain more common causes of viral encephalitis and must be ruled out 1