title: Recurrent tuberculosis in Denmark: relapse vs. re-infection.
abstract: METHODS
  Denmark, a country with a low-incidence of tuberculosis (TB).
  
  
  OBJECTIVE
  To analyse the proportion of relapse vs. re-infection and to compare selected characteristics between the two subgroups.
  
  
  METHODS
  A population-based cohort study. All 4154 Mycobacterium tuberculosis isolates from patients in Denmark genotyped by insertion sequence 6110 restriction fragment length polymorphism were followed for recurrent TB over 13.5 years. Recurrent cases were classified as relapse or re-infection by genotype patterns in initial and serial disease episodes.
  
  
  RESULTS
  Recurrent TB was found in 73 (1.8%) cases. Identical M. tuberculosis genotypes in initial and serial episodes were found in 54 (1.3%), indicating relapse, whereas different genotypes, representing re-infection, were found in 19 (0.5%) cases. Cavitary TB in the initial episode was significantly associated with relapse (OR 4.6, 95%CI 1.1-26.9) compared to re-infection.
  
  
  CONCLUSIONS
  The rate of recurrent TB is low in Denmark. Comparing selected characteristics between the relapse and re-infection subgroups revealed that only the presence of cavitary disease was associated with relapse. Although recurrent TB was rarely due to re-infection, the risk of re-infection increased with time.
authors.affiliation: International Reference Laboratory of Mycobacteriology, National Centre for Antimicrobials and Infection Control, Statens Serum Institut, Copenhagen, Denmark. dvb@ssi.dk
authors.forename: D
authors.initials: D
authors.lastname: Bang
authors.forename: A B
authors.initials: AB
authors.lastname: Andersen
authors.forename: V O
authors.initials: VO
authors.lastname: Thomsen
authors.forename: T
authors.initials: T
authors.lastname: Lillebaek
mesh_terms: D000328:Adult; D000995:Antitubercular Agents / Q000627:therapeutic use; D015373:Bacterial Typing Techniques; D015331:Cohort Studies; D004269:DNA, Bacterial / Q000302:isolation & purification; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000235:genetics; D016017:Odds Ratio; D012150:Polymorphism, Restriction Fragment Length; D011159:Population Surveillance; D012008:Recurrence; D018570:Risk Assessment; D013997:Time Factors; D016896:Treatment Outcome; D014376:Tuberculosis / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D055815:Young Adult
chemical_list: D000995:Antitubercular Agents; D004269:DNA, Bacterial