Common and Clinically Significant Legionella pneumophila Sequence Types (STs) Sequence types (STs) are genetic fingerprints used to identify and track Legionella pneumophila strains involved in outbreaks and clinical disease. Below are the most common and medically important STs documented worldwide. 1. ST1 — Dominant Global Strain Most common ST worldwide Represents 25–40% of all Legionnaires’ disease cases Found in hospitals, hotels, cooling towers, and potable water Highly persistent and virulent 2. ST23 — Major European & U.S. Clinical Strain Common in Italy, France, Spain, and the U.S. Seen in both travel-associated and community-acquired infections 3. ST37 — Healthcare-Associated Frequently isolated from hospital water systems Linked to infections in immunocompromised patients 4. ST62 — Cooling-Tower Associated A major contributor to large community outbreaks Common worldwide 5. ST47 — Internationally Significant Involved in frequent travel-associated clusters Found in potable water and cooling towers 6. ST42 — Persistent in Hospitals Recurrently detected in healthcare water systems Colonizes biofilms effectively 7. ST5 — Healthcare-Focused Strain Often infects long-term care and immunocompromised populations 8. ST36 — Historical U.S. Outbreak Strain Responsible for the 1976 Philadelphia outbreak Still found in U.S. cooling towers Honorable Mentions ST187 — Outbreaks in Germany and Northern Europe ST211 — Emerging in Canada and Europe ST260 / ST263 — Clinically severe but less common ST93 & ST8 — Travel-associated clusters Summary: The “Big 8” Clinically Important STs ST1 ST23 ST37 ST62 ST47 ST42 ST5 ST36 Why These STs Cause More Disease Strong growth inside amoeba (environmental hosts) Efficient macrophage infection in humans Resistance to heat, chlorine, copper–silver, and stagnation Expression of potent virulence factors (e.g., Dot/Icm system, mip) Request Proposal Contact Us
