Influenza and Epstein-Barr virus encephalitis in children: could we be missing them and why?

We note the case of influenza A encephalopathy reported in the Hong Kong Medical Journal in 2020, involving an unvaccinated 10-year-old child who presented with high fever, convulsions, and altered consciousness. 1 The patient was successfully treated with anticonvulsants, oseltamivir, and hypertonic saline and mannitol to control cerebral oedema.The electroencephalogram showed diffuse slow-wave activity. 1 Although Hong Kong offers a free seasonal influenza vaccination programme for children aged 6 months to under 12 years (those attending primary school), uptake remains relatively low (50%-60%), 2 and several paediatric influenza-related deaths are reported annually in the city, primarily among unvaccinated children. 3 A diagnosis of influenza encephalitis is made after exclusion of all other possible causes, following confirmed detection of influenza virus in a respiratory sample, but only very rarely by detection of influenza RNA in the cerebrospinal fluid (CSF).Clinical presentation can be variable, including fever, seizures, meningism, photophobia, excessive sleepiness, disorientation, agitation, altered personality, and leg paresis.Electroencephalogram findings can show diffuse slowing or generalised spike-wave activity, while magnetic resonance imaging may be normal or show multiple focal lesions.4 This form of 'indirect' diagnosis in viral encephalitis is not unique to influenza.Among other viral encephalitis-such as West Nile virus, Japanese encephalitis virus, and tick-borne encephalitis viruses-diagnosis is often confirmed by serology or seroconversion as the virus may have already cleared from the CSF by the time patients with neurological symptoms present.Concerning influenza encephalitis, virus detection in a respiratory sample by polymerase chain reaction is a common diagnostic approach.Treatment of influenza in otherwise healthy children is often not required; whether treated or not, the clinical outcomes of presumed influenza encephalitis are generally good, especially when oseltamivir and neurosupportive treatment are promptly instituted.5 A practical diagnostic distinction has been