title: Characteristics of non-clustered tuberculosis in a low burden country.
abstract: Molecular genotyping studies often focus on clustered tuberculosis and recent transmission. Less attention has been paid to non-clustered tuberculosis. However, non-clustered cases also contribute significantly to the tuberculosis burden, especially in low-incidence countries. The objective of this study is to characterize non-clustered tuberculosis cases in Denmark and point out potential implications for tuberculosis control. The study is based on nationwide IS6110-RFLP genotyping of tuberculosis cases from 1992 through 2004, corresponding to 98% of culture verified cases. Of 3988 cases, 45% were non-clustered. Both Danes and immigrants had a peak incidence of non-clustered tuberculosis at older ages, 80-89 years (4.3 cases/10(5) population/year) and 60-69 years (28.8 cases/10(5) population/year), respectively. In addition, immigrants had a peak at 20-29 years (43.2 cases/10(5) inhabitants/year). In Danes, the incidence of non-clustered tuberculosis decreased during the study period and was predominantly found in elderly persons, presumably reactivating infection acquired during 1910-40, when tuberculosis incidence was high. In immigrants, the incidence was high at all ages, presumably reflecting reactivation of imported infections. In the future, the number of non-clustered tuberculosis cases will decrease, as older Danes die, and as time since primary infection increases for immigrants residing in Denmark. TB control should include focus on non-clustered cases.
authors.affiliation: International Reference Laboratory of Mycobacteriology, Statens Serum Institut, 5 Orestads Boulevard, DK-2300 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: Ib Christian
authors.initials: IC
authors.lastname: Bygbjerg
authors.forename: Vibeke Ostergaard
authors.initials: VO
authors.lastname: Thomsen
authors.forename: Troels
authors.initials: T
authors.lastname: Lillebaek
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005838:Genotype; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000235:genetics; D012150:Polymorphism, Restriction Fragment Length; D012189:Retrospective Studies; D017678:Sex Distribution; D014171:Transients and Migrants / Q000706:statistics & numerical data; D014376:Tuberculosis / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D055815:Young Adult