Clustered tuberculosis in a low-burden country: nationwide genotyping through 15 years

J Clin Microbiol. 2012 Aug;50(8):2660-7. doi: 10.1128/JCM.06358-11. Epub 2012 Jun 6.


Molecular genotyping of Mycobacterium tuberculosis has proved to be a powerful tool in tuberculosis surveillance, epidemiology, and control. Based on results obtained through 15 years of nationwide IS6110 restriction fragment length polymorphism (RFLP) genotyping of M. tuberculosis cases in Denmark, a country on the way toward tuberculosis elimination, we discuss M. tuberculosis transmission dynamics and point to areas for control interventions. Cases with 100% identical genotypes (RFLP patterns) were defined as clustered, and a cluster was defined as cases with an identical genotype. Of 4,601 included cases, corresponding to 76% of reported and 97% of culture-verified tuberculosis cases in the country, 56% were clustered, of which 69% were Danes. Generally, Danes were more often in large clusters (≥ 50 persons), older (mean age, 45 years), and male (male/female ratio, 2.5). Also, Danes had a higher cluster frequency within a 2-year observation window (60.8%), and higher clustering rate of new patterns over time, compared to immigrants. A dominant genotype, cluster 2, constituted 44% of all clustered and 35% of all genotyped cases. This cluster was primarily found among Danish males, 30 to 59 years of age, often socially marginalized, and with records of alcohol abuse. In Danes, cluster 2 alone was responsible for the high cluster frequency level. Immigrants had a higher incidence of clustered tuberculosis at a younger age (0 to 39 years). To achieve tuberculosis elimination in Denmark, high-risk transmission environments, like the cluster 2 environment in Danes, and specific transmission chains in immigrants in the capital area, e.g., homeless/socially marginalized Somalis/Greenlanders, often with alcohol abuse, must be targeted, including groups with a high risk of reactivation.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Child
  • Child, Preschool
  • Cluster Analysis
  • DNA Transposable Elements
  • DNA, Bacterial / genetics
  • Denmark / epidemiology
  • Female
  • Genotype
  • Humans
  • Infant
  • Infant, Newborn
  • Male
  • Middle Aged
  • Molecular Epidemiology
  • Molecular Typing*
  • Mycobacterium tuberculosis / classification*
  • Mycobacterium tuberculosis / genetics*
  • Mycobacterium tuberculosis / isolation & purification
  • Polymorphism, Restriction Fragment Length
  • Retrospective Studies
  • Tuberculosis / epidemiology*
  • Tuberculosis / microbiology*
  • Young Adult


  • DNA Transposable Elements
  • DNA, Bacterial