Successful treatment with oseltamivir of an atypical influenza B-associated encephalitis identified by mNGS: A case report.

This case report describes a 51-year-old female with influenza B-associated encephalitis (IBAE) presenting primarily with insomnia, headache, and dizziness, but without fever, following an initial cough. Routine microbiological tests (cultures, staining, multiplex PCR) on cerebrospinal fluid (CSF) and initial brain/chest CT scans were negative. Diagnosis was confirmed by metagenomic next-generation sequencing (mNGS) detecting influenza B virus in the CSF. Treatment involved oral oseltamivir and fluid replacement for headache/intracranial pressure. Symptoms significantly improved after eight days of oseltamivir, leading to discharge. This case highlights sleep disturbances and headache as primary IBAE symptoms without fever. Routine CSF testing often fails to detect influenza B; early mNGS enables definitive diagnosis, allowing precise, timely treatment (like oseltamivir) and avoiding ineffective empiric therapy or disease worsening.