Emergency Department Presentations of West Nile Virus.

INTRODUCTION

Maricopa County, Arizona, experienced its largest West Nile virus outbreak in 2021, with 1,487 cases and 101 deaths, in the midst of the COVID-19 pandemic. We sought to describe initial presentations of emergency department (ED) patients ultimately diagnosed with West Nile virus and determine how often patients presented to the ED before their diagnosis. To assist with disease recognition during future outbreaks, we examined in detail cases where emergency physicians initially did not suspect West Nile virus.

METHODS

We reviewed records from May-December 2021 for patients with a positive West Nile virus result and at least one ED visit within 15 days. Data included age, sex, race, Emergency Severity Index (ESI) score, number of ED visits, chief complaint, vital signs, blood or cerebrospinal fluid (CSF) testing, diagnosis, and disposition. We excluded cases with only immoglobulin G-positive results or outpatient tests, leaving 147 cases.

RESULTS

Among 147 ED West Nile virus cases, the median patient age was 67 years, with patients being predominantly male (66.7%) and White (97.3%). The most common presenting chief complaints included fever (23.8%), headache (17.7%), and generalized weakness (11.6%). Emergency physicians initiated testing for the virus in 63 cases (42.9%). Patients dispositioned (n = 84, either discharged or admitted) from the ED without initiation of testing tended to be older (median 73 vs 62 years, P < .001), with higher triage respiratory rate (mean 19.4 vs 18.3 breaths per minute, P = .05) and lower triage oxygen saturation (median 96% vs 97%; P =.02). Emergency physicians predominantly performed CSF testing (n = 42 patients) over serum testing (n = 21 patients). Patients tested via CSF had lower ESI scores than those tested via serum (ESI score of 1-2 45.3% vs 14.3%, P = .03).

CONCLUSION

Emergency physicians did not initiate testing in 57.1% of initial ED encounters of patients ultimately found to have West Nile virus. During West Nile virus outbreaks, emergency physicians should stay vigilant for less acute presentations, such as generalized weakness in elderly patients, along with typical presentations including fever and headache, to avoid delayed diagnosis.