# Powassan and Eastern Equine Encephalitis Virus Seroprevalence in Endemic Areas, United States, 2019–2020

## TL;DR

This study measured how common Powassan and Eastern equine encephalitis viruses are in blood donors from areas where these viruses are common in the U.S.

## Contribution

The study provides new seroprevalence data for two arboviruses in endemic U.S. regions, highlighting potential transmission risks through blood transfusions and organ donations.

## Key findings

- Powassan virus seroprevalence ranged from 0% to 11.5% across four states.
- Eastern equine encephalitis virus was detected in one county with an estimated seroprevalence of 1.62%.
- Low overall seroprevalence suggests limited transmission risk, but higher-prevalence areas may need further study.

## Abstract

Powassan virus (POWV) and Eastern equine encephalitis virus (EEEV) are regionally endemic arboviruses in the United States that can cause neuroinvasive disease and death. Recent identification of EEEV transmission through organ transplantation and POWV transmission through blood transfusion have increased concerns about infection risk. After historically high numbers of cases of both viruses were reported in 2019, we conducted a seroprevalence survey using blood donation samples from selected endemic counties. Specimens were screened for virus-specific neutralizing antibodies, and population seroprevalence was estimated using weights calibrated to county population census data. For POWV, median county seroprevalence in 4 states was 0.84%, ranging from 0% (95% CI 0%–2.28%) to 11.5% (95% CI 0.82%–40.9%). EEEV infection was identified in a single county (estimated seroprevalence 1.62% [95% CI 0.04%–8.75%]). Although seroprevalence estimates in sampled areas were generally low, additional investigation of higher-prevalence areas could inform risk for transmission from asymptomatic blood and organ donors.