title: Tuberculosis in contacts need not indicate disease transmission.
abstract: BACKGROUND
  Traditional contact investigation is an important tool for controlling tuberculosis. It may also help to indicate drug susceptibility patterns when Mycobacterium tuberculosis cultures are not available. Such investigations often underestimate the degree of transmission found by genotyping, but overestimation may also occur. This report is the result of a routine successive DNA restriction fragment length polymorphism (RFLP) analysis of M tuberculosis isolated in Norway.
  
  
  METHODS
  Fifteen immigrants belonging to the same community were notified with tuberculosis during February to September 2003. The mycobacterial isolates were analysed by RFLP.
  
  
  RESULTS
  All 15 patients had social contact with each other and 13 belonged to the same church community. A total of 14 cultures were positive for M tuberculosis. Among these isolates, six different genotypes were found. Five patients had not acquired the infection from the putative source.
  
  
  CONCLUSIONS
  Reactivation of tuberculosis may occur in contacts during the development of an outbreak. In such situations, traditional contact investigations may overestimate the rate of transmission found by genotyping of M tuberculosis. When cultures are unavailable and presumed drug susceptibility patterns are based on that of contacts, such overestimation may lead to incorrect treatment of a patient. Contact investigations must be combined with genotyping of M tuberculosis to conclude how tuberculosis is transmitted. This is especially important in persons with several risk factors for infection.
authors.affiliation: Division of Infectious Disease Control, Norwegian Institute of Public Health, P O Box 4404, Nydalen, N-0403 Oslo, Norway. ulf.dahle@fhi.no
authors.forename: U R
authors.initials: UR
authors.lastname: Dahle
authors.forename: S
authors.initials: S
authors.lastname: Nordtvedt
authors.forename: B A
authors.initials: BA
authors.lastname: Winje
authors.forename: T
authors.initials: T
authors.lastname: Mannsaaker
authors.forename: E
authors.initials: E
authors.lastname: Heldal
authors.forename: P
authors.initials: P
authors.lastname: Sandven
authors.forename: H M S
authors.initials: HM
authors.lastname: Grewal
authors.forename: D A
authors.initials: DA
authors.lastname: Caugant
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D016358:Contact Tracing; D004269:DNA, Bacterial / Q000235:genetics; D004641:Emigration and Immigration; D005260:Female; D005838:Genotype; D006801:Humans; D007223:Infant; D008297:Male; D009169:Mycobacterium tuberculosis / Q000235:genetics*; D009664:Norway; D012150:Polymorphism, Restriction Fragment Length; D012307:Risk Factors; D014376:Tuberculosis / Q000235:genetics / Q000635:transmission*
chemical_list: D004269:DNA, Bacterial