Active Public Health Outbreaks: Wyoming
Surveillance Report • November 30, 2025
Critical Alert
Norovirus Surge
Status: HIGH ACTIVITY
Wyoming is currently identified as a hotspot for a national norovirus surge. Emergency department visits for gastrointestinal illness have spiked significantly since July, with positive test rates doubling nationally from August to November.
Ongoing Monitoring
Measles Resurgence
Status: ACTIVE CLUSTERS
After over a decade with zero cases, Wyoming confirmed 9 cases in 2025 (Jan–Sept). The outbreak, centered in Carbon, Natrona, and Niobrara counties, is linked primarily to unvaccinated residents.
Respiratory Virus Season (2025-2026)
As of late November 2025, Wyoming is entering the respiratory virus season. While influenza activity remains low, early indicators suggest rising transmission for COVID-19 and RSV.
Detailed Outbreak Analysis
Pertussis (Whooping Cough)
2025 Impact: Significant increase over previous years.
Wyoming experienced a sharp rise in pertussis cases in 2025. By March alone, 30 confirmed cases were reported, compared to zero in 2023. The outbreak has affected multiple counties including Sheridan, Campbell, Johnson, and Lincoln. Public health officials warn that actual numbers are likely much higher due to underreporting and undiagnosed mild cases in adults.
Avian Influenza (H5N1)
2025 Impact: First confirmed human case in state history.
In February 2025, Wyoming confirmed its first human case of H5N1 "Bird Flu" in an older adult from Platte County who had contact with infected backyard poultry. While the case was severe, requiring hospitalization, the CDC and Wyoming Department of Health maintain that the risk to the general public remains low. No human-to-human transmission has been documented in this event.
Data Discrepancies & Context
Reported vs. Actual
Pertussis & Flu: Official counts are widely considered underestimates. Many adults with pertussis present with only a lingering cough and do not seek testing, yet remain infectious to vulnerable infants.
Vaccination Status
Measles: The 2025 outbreak is explicitly linked to vaccination gaps. Of the initial cluster, 6 out of 7 cases were unvaccinated individuals, highlighting pockets of vulnerability in community immunity.
Risk Communication
Bird Flu: A contrast exists between the high mortality in infected poultry/mammals and the "low risk" messaging for humans. Officials emphasize that risk is primarily occupational (farm workers, backyard flock owners).
Data Sources: Wyoming Department of Health (WDH), Centers for Disease Control and Prevention (CDC), and local surveillance reports. Data current as of November 30, 2025.