Indications for JEV testing

The following communiqué has been released by the Darling Downs Public Health Unit (PHU).

Darling Downs PHU has been notified of a large number of JEV test requests in recent cooler months. Many of these are for non-specific illnesses, or for patients who do not have a headache or a fever, or an acute illness.

To meet the case definition for non-encephalitic JEV disease, a patient would need to have headache and a fever, alongside suggestive results (JEV investigations should be considered for all patients with severe symptoms indicating encephalitic disease, but these patients will likely be in hospital and worked up from there).

As per the Queensland Health guidelines (Japanese encephalitis | Queensland Health) clinical evidence for JEV includes:

1. Encephalitic illness: acute meningoencephalitis characterised by one or more of the following:

• Focal neurological disease, or seizures, or acute impairment in level of consciousness
• An abnormal CT or MRI or EEG consistent with flavivirus encephalitis
• Presence of pleocytosis in CSF

2. Non-encephalitic illness: Acute febrile illness with headache, with or without myalgia or rash.

Other points to note:

• Only ~1% of JEV infections cause symptomatic illness, with fewer than this causing severe/encephalitic disease
• In children gastrointestinal pain and vomiting may be the initial dominant symptoms.
• Given that clinical disease is rare, there is a low pre-test probability of a positive JEV test result. However, requesting clinicians should consider a patient’s possible exposure in the 2 weeks prior to onset of symptoms (e.g. to mosquitoes or pigs in Australia or overseas) and whether there have been known JEV detections in the area(s) where the patient has been (reflected in vaccine eligibility).
• Confirming a case on pathology testing can be difficult for JEV:
  • PCR detection is very rare due to the brief and very low level of viraemia in humans (would only possibly be positive in the first week after onset of symptoms, and even then in <1% of cases)
  • Serology can be difficult to interpret due to cross-reactivity with flaviviruses and other infections, or flavivirus vaccination causing false positives.
• Many patients will have prior immunity from vaccination or past infection (even if asymptomatic). Serological testing to determine immunity is not recommended.

Please consider whether JEV testing is appropriate in patients without encephalitis, or without fever and headache.

This may be an opportune time to inform your patient about the free (if eligible), safe, and effective JEV vaccine.

Note: if requesting JEV testing, please document the salient clinical features e.g. acute febrile illness with headache, exposure, and onset date. It is additionally helpful to include if the patient has been vaccinated for JEV or yellow fever.

If there is any doubt about whether testing should be performed or not, or any other enquiries relating to this, please do not hesitate to contact the Darling Downs Public Health Unit (07 4699 8240) or an infectious diseases team.