Florida Improves West Nile Virus Detection


  • In 2020, Florida had its third-highest number of reported cases of West Nile virus (WNV).
  • The Florida Department of Health recognized the need to detect WNV early at hospitals where people seek care.
  • The Florida Department of Health compared reported disease cases with automated, electronic health data from emergency department (ED) visits.
A digital rendering of a mosquito

Public health problem

In 2020, Florida experienced increased West Nile virus (WNV) activity resulting in the third-highest number of reported cases on record in the state. WNV disease case identification is challenging because symptoms can be nonspecific and mimic other health conditions. The Florida Department of Health sought to improve the existing definitions used to search emergency department data, thereby increasing the likelihood of detecting WNV.

Actions taken

The Florida Department of Health reviewed 2020 WNV disease case records (confirmed and probable) to identify commonly reported chief complaints (CCs) and discharge diagnoses (DDs). Medical records uploaded to Florida's reportable disease surveillance system were used to determine CCs and DDs of WNV disease cases meeting the Council of State and Territorial Epidemiologists' current case definition. Commercial testing of all reported cases was confirmed at a reference laboratory. The CCs and DDs identified in medical records were compared to those in Florida's syndromic surveillance system, the Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE–FL).


Of the 46 WNV disease cases, 39 patients had medical records available for review. Of those, the most common CCs were fever (59%), weakness (33%), and altered mental status (AMS; 28%). Additionally, one patient (3%) presented with CC of falls. The most common DDs were fever (54%), AMS (33%), meningitis (33%), encephalitis (28%), and weakness (21%). Two patients (5%) had falls listed as DDs.

Only five patients (13%) had DDs that included WNV. Additionally, one patient not initially diagnosed with WNV disease was identified through ESSENCE–FL based on the reported symptoms (meningitis and AMS).

Other DDs included sepsis (15%); urinary tract infections (5%); and kidney (13%), pulmonary (8%), and cardiac (5%) issues. ESSENCE–FL listed more DDs than were found in the medical records, perhaps due to updates over time. These findings suggest that by searching emergency department data and by refining the queries, the Florida Department of Health can identify unreported WNV disease.

A review of CCs of patients presenting with the following symptoms may be useful for detecting WNV disease: fever and weakness; fever and AMS; fever, weakness, and AMS; and DDs of fever with AMS, meningitis, encephalitis, or weakness, potentially in conjunction with patient age. In addition, DDs provided information not captured in the medical records provided to the health department.


Catherine McDermott, MPH, MHS
Multi-County Epidemiologist
Florida Department of Health in Levy County
Email: Catherine.McDermott@flhealth.gov

Andrea Morrison, PhD
Vector-Borne Disease Surveillance Coordinator
Florida Department of Health
Division of Disease Control and Health Protection
Bureau of Epidemiology
Email: Andrea.Morrison@flhealth.gov

Centers for Disease Control and Prevention
Office of Public Health Data, Surveillance, and Technology
Detect and Monitor Division

The findings and outcomes described in this syndromic success story are those of the authors and do not necessarily represent the official position of the National Syndromic Surveillance Program or the Centers for Disease Control and Prevention.