Testing and Diagnosis for Powassan Virus Disease: A Guide for Clinicians

Powassan virus is spread mainly by Ixodes ticks and, rarely, through blood transfusion. CDC's guidance for health care providers explains how the disease is diagnosed. In short: antibody (serologic) testing is the main method, a positive IgM result should be confirmed by neutralizing antibody testing at a state public health laboratory or CDC, and state or local health departments can help arrange testing.

Preliminary diagnosis

A preliminary diagnosis rests on the patient's clinical signs and symptoms, where the infection was likely acquired — including places and dates of travel — and activities that could have exposed them to the virus.

Powassan virus disease is nationally notifiable, and every case should be reported to local public health authorities. Reports help local, state and national authorities spot outbreaks and take steps to prevent further infections.

Laboratory testing

Diagnosis is usually made by testing serum or cerebrospinal fluid (CSF) for Powassan virus-specific IgM and neutralizing antibodies.

1. IgM capture ELISA. The first test, available commercially, at some state health departments and at CDC.
2. Plaque-reduction neutralization test (PRNT). A positive IgM result should be confirmed by neutralizing antibody testing of serum at a state public health laboratory or CDC.

Some tests are not always available at CDC; its Test Directory lists which ones it currently performs.

Patients who may need molecular testing

Some immunocompromised patients may need other tests:

• RT-PCR can detect viral RNA in serum, CSF and tissue collected early in the illness; a positive result confirms infection.
• Immunohistochemistry (IHC) can detect viral antigen in formalin-fixed tissue.
• These tests are done at CDC and some state public health or reference laboratories. A negative result does not rule out infection.

Sending specimens

To submit specimens, contact the state or local health department, which can help decide whether samples should go to the CDC Arbovirus Diagnostic Laboratory. Specimens reach CDC through state health departments, and CDC sends all results back to the state health department.

Sources

• Centers for Disease Control and Prevention, "Clinical Testing and Diagnosis for Powassan Virus Disease": https://www.cdc.gov/powassan/hcp/diagnosis-testing/index.html