Active Public Health Outbreaks in Colorado
Surveillance Report • November 30, 2025
Highest Alert
Pertussis
Active outbreak at CSU; statewide cases >700.
Rising Quickly
Influenza
Season arrived early; pediatric hospitalizations ticking up.
Monitored
Avian Flu (H5N1)
10 cumulative human cases; risk remains low.
ACTIVE OUTBREAK Pertussis (Whooping Cough)
As of late November 2025, Colorado is experiencing a significant resurgence of Pertussis, commonly known as whooping cough. Unlike the respiratory viral season which fluctuates annually, this bacterial outbreak represents a distinct "return to baseline" after pandemic-era lows, but with a sharper recent spike.
Current Situation Report
- Fort Collins Cluster: Colorado State University (CSU) has confirmed an active outbreak with 14 confirmed cases in the Fall 2025 semester alone.
- Statewide Trend: Total cases for 2025 have exceeded 700, surpassing the ~600 cases recorded by this time in 2024 and significantly higher than the ~200 cases in 2023.
- Risk Factors: Health officials note a "noticeable jump" as students returned to school. The infection is particularly dangerous for infants and immunocompromised adults.
Respiratory Virus Surveillance
The 2025-2026 respiratory season has begun with an early arrival of Influenza, while COVID-19 activity remains relatively stable. The Colorado Department of Public Health and Environment (CDPHE) is utilizing a unified dashboard to track these trends.
| Pathogen | Status (Nov 2025) | Trend |
|---|---|---|
| Influenza (Flu) | Early season onset; rising emergency room visits. | ? Increasing |
| COVID-19 | "Staying chill"; lowest seasonal numbers since pandemic. | ? Stable |
| RSV | Pediatric hospitalizations increasing; typical seasonal pattern. | ? Moderate Rise |
| Norovirus | Slower start in CO compared to national surge. | ? Monitoring |
Avian Influenza (H5N1)
Status: Stable / Monitored
Colorado has recorded approximately 10 human cases of H5N1 bird flu in 2025, primarily among poultry workers involved in culling operations. While the CDC assesses the risk to the general public as low, the state remains a focal point for monitoring due to its significant dairy and poultry industries. No sustained human-to-human transmission has been detected.
Resolved: E. coli (McDonald's)
Status: Investigation Closed / Inactive
A major outbreak linked to slivered onions on McDonald's Quarter Pounders occurred in October 2024. It resulted in 26 cases and one death in Colorado. While educational sessions (e.g., ECHO Colorado) are reviewing this event in November 2025, the outbreak itself is not currently active.