Adult Invasive Haemophilus influenzae Type b Cluster – King County, Washington State, 2024 — 2025
- Presentation Day/Time: Friday, April 24, 9:05 AM
- Presenter: Camerin Rencken, PhD, ScM, Washington State Department of Health
The Issue
- In March 2024, a King County hospital notified Public Health–Seattle & King County and the Washington State Department of Health of an increase in adult invasive Haemophilus influenzae infections. At that time, invasive H. influenzae among adults was not notifiable in Washington.
What We Did
- We investigated to characterize the outbreak, assess trends, and guide prevention efforts.
What We Found
- We identified 26 adult cases of H. influenzae type b (Hib) during March 2024–December 2025. Most patients reported current housing instability (84%) and substance use (93%), and whole genome sequencing showed that all of the isolates were closely related. Since becoming notifiable at the start of 2026, 16 additional adult cases have been reported.
What This Means
- Enhanced surveillance and serotyping of invasive H. influenzae in adults may help identify epidemiologic shifts, risk factors, and prevention opportunities.
