title: Risk of active tuberculosis among schoolchildren in Hong Kong.
abstract: OBJECTIVE
  To estimate the risk of active tuberculosis (TB) and its implication on preventive treatment among BCG-vaccinated schoolchildren.
  
  
  METHODS
  Cohort and case-control designs.
  
  
  METHODS
  Community settings in a high-prevalence area.
  
  
  METHODS
  Children in primary school. The main exposure was their tuberculin response.
  
  
  METHODS
  Of 94,928 primary schoolchildren tuberculin tested during a routine school revaccination program in 1999, 656 with a tuberculin response at 20 mm or more were followed up prospectively through the territory-wide TB registry up to December 31, 2003, for the development of TB. In a separate case-control analysis, the tuberculin responses of children who subsequently had active TB (at the age of 10-15 years) were compared with those of their sex- and age-matched classmates to ascertain the relative risks of TB for different tuberculin reaction categories. The absolute and relative risks were applied to the 1999 cohort for estimating the incidence of TB among different tuberculin reactors.
  
  
  RESULTS
  The annual incidence (95% confidence interval) of active TB was estimated to be 13.4 (5.6-40.6) per 100,000 for the entire cohort and 7.5 (2.4-24.5), 7.5 (1.7-32.0), 16.0 (4.4-57.2), 92.6 (26.6-320.2), and 340.6 (163.3-626.4) per 100,000 for children with a tuberculin reaction at 0 to 4, 5 to 9, 10 to 14, 15 to 19, and 20 mm or more, respectively. By using 10 mm as the cutoff, 482 (95% confidence interval, 163-1391) children have to be treated to prevent a single case of active TB within 5 years. Treatment will cover 17.5% of the cohort, but prevent only 54.1% of all active TB cases.
  
  
  CONCLUSIONS
  It is desirable to reexamine the existing screening method for BCG-vaccinated children from high-prevalence countries.
authors.affiliation: Tuberculosis and Chest Service, Department of Health, Hong Kong. cc_leung@dh.gov.hk
authors.forename: Chi Chiu
authors.initials: CC
authors.lastname: Leung
authors.forename: Wing Wai
authors.initials: WW
authors.lastname: Yew
authors.forename: Kwok Chiu
authors.initials: KC
authors.lastname: Chang
authors.forename: Cheuk Ming
authors.initials: CM
authors.lastname: Tam
authors.forename: Chi Kuen
authors.initials: CK
authors.lastname: Chan
authors.forename: Wing Sze
authors.initials: WS
authors.lastname: Law
authors.forename: Man Yee
authors.initials: MY
authors.lastname: Wong
authors.forename: Shuk Nor
authors.initials: SN
authors.lastname: Lee
authors.forename: Maria
authors.initials: M
authors.lastname: Leung
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D017678:Sex Distribution; D013334:Students / Q000706:statistics & numerical data*; D014373:Tuberculin / Q000276:immunology; D014374:Tuberculin Test; D014376:Tuberculosis / Q000453:epidemiology* / Q000276:immunology
chemical_list: D014373:Tuberculin