Migration and tuberculosis transmission in Hamburg, Germany: insights from 25 years of molecular epidemiology.

Migration increases the genetic diversity of Mycobacterium tuberculosis complex strains in Hamburg but does not change local transmission patterns, which remain lineage-specific.

• Why it matters: Understanding how imported strains influence TB transmission is crucial for controlling outbreaks in low-incidence settings, especially as migration alters population composition.
• What they did: Whole genome sequencing of 3,131 strains collected over 25 years was used to analyze population structure and transmission dynamics in relation to patients' origins, revealing shifts in lineage distribution.
• The result: Despite increased diversity from migration, transmission was mainly driven by established L4 strains and their sublineages, supporting the idea that successful transmission involves locally adapted sublineages.