Cerebrospinal Fluid Testing for Neuroinvasive West Nile Virus and Measures to Improve Guideline Adherence

**Background**

Diagnosis of West Nile virus (WNV) neuroinvasive disease, an important cause
of neurologic disability in endemic areas, requires appropriate testing given
its nonspecific presentation. Guidelines recommend cerebrospinal fluid (CSF)
testing of WNV-specific immunoglobulin M (IgM) in all patients, with
additional reverse transcription-polymerase chain reaction (RT-PCR) testing
only in those who are unable to mount a humoral response due to significant
immunosuppression. WNV testing is known to be underutilized, but provider
choice between the appropriate IgM test and lower sensitivity RT-PCR test when
both are readily available has not been described.

**Methods**

We analyzed testing patterns for suspected neuroinvasive WNV in a
retrospective analysis of 1304 adult patients in a Boston hospital network who
underwent CSF testing of WNV-specific IgM or WNV RNA using RT-PCR between 2016
and 2023. Both CSF IgM and RT-PCR were available to order during the duration
of the study. Relevant clinical, laboratory, and demographic data were
extracted from the electronic health record (EHR).

**Results**

The median age in our cohort was 63 years, and 46% of patients were female.
Sole testing with CSF RT-PCR occurred in 73% of patients, and WNV testing
guidelines were adhered to in only 26% of cases. Elevated CSF protein, CSF
lymphocytic pleocytosis, admission to a neurology service, immunocompetence,
race, and hospital site were significantly associated with improved adherence.
WNV tests were positive in 26 patients, and patients whose CSF testing
patterns adhered to guidelines were 12 times more likely to receive a WNV
diagnosis.

**Discussion**

The existence of guidelines for appropriate diagnostic testing may not be
sufficient to encourage appropriate CSF WNV IgM testing when the RT-PCR test,
which is not recommended in immunocompetent patients, remains readily
available for ordering. Differential guideline adherence based on
institutional factors suggests that systems changes may play an important role
in shaping provider behavior around appropriate use of diagnostic testing.