title: Migrant tuberculosis: the extent of transmission in a low burden country.
abstract: BACKGROUND
  Human migration caused by political unrest, wars and poverty is a major topic in international health. Infectious diseases like tuberculosis follow their host, with potential impact on both the migrants and the population in the recipient countries. In this study, we evaluate Mycobacterium tuberculosis transmission between the national population and migrants in Denmark.
  
  
  METHODS
  Register study based on IS6110-RFLP results from nationwide genotyping of tuberculosis cases during 1992 through 2004. Cases with 100% identical genotypes were defined as clustered and part of a transmission chain. Origin of clusters involving both Danes and migrants was defined as Danish/migrant/uncertain. Subsequently, the proportion of cases likely infected by the "opposite" ethnic group was estimated.
  
  
  RESULTS
  4,631 cases were included, representing 99% of culture confirmed cases during 1992 through 2004. Migrants contributed 61.6% of cases. Up to 7.9% (95% CI 7.0-8.9) of migrants were infected by Danes. The corresponding figure was 5.8% (95% CI 4.8-7.0) for Danes. Thus, transmission from Danes to migrants occurred up to 2.5 (95% CI 1.8-3.5) times more frequent than vice versa (OR = 1). A dominant strain, Cluster-2, was almost exclusively found in Danes, particular younger-middle-aged males.
  
  
  CONCLUSIONS
  Transmission between Danes and migrants is limited, and risk of being infected by the "opposite" ethnic group is highest for migrants. TB-control efforts should focus on continues micro-epidemics, e.g. with Cluster-2 in Danes, prevention of reactivation TB in high-risk migrants, and outbreaks in socially marginalized migrants, such as Somalis and Greenlanders. Fears that TB in migrants poses a threat for resident Danes seem exaggerated and unjustified. We believe this to be true for other low incidence countries as well.
authors.affiliation: International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark. zazakj@me.com
authors.forename: Zaza
authors.initials: Z
authors.lastname: Kamper-Jørgensen
authors.forename: Aase Bengaard
authors.initials: AB
authors.lastname: Andersen
authors.forename: Axel
authors.initials: A
authors.lastname: Kok-Jensen
authors.forename: Mads
authors.initials: M
authors.lastname: Kamper-Jørgensen
authors.forename: Ib Christian
authors.initials: IC
authors.lastname: Bygbjerg
authors.forename: Peter Henrik
authors.initials: PH
authors.lastname: Andersen
authors.forename: Vibeke Ostergaard
authors.initials: VO
authors.lastname: Thomsen
authors.forename: Troels
authors.initials: T
authors.lastname: Lillebaek
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016000:Cluster Analysis; D004251:DNA Transposable Elements; D003718:Denmark / Q000453:epidemiology; D018562:Disease Transmission, Infectious; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D017720:Molecular Epidemiology; D058889:Molecular Typing; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D012150:Polymorphism, Restriction Fragment Length; D014171:Transients and Migrants; D014376:Tuberculosis / Q000453:epidemiology* / Q000635:transmission*
chemical_list: D004251:DNA Transposable Elements