title: Changing prevalence of tuberculosis infection with increasing age in high-burden townships in South Africa.
abstract: METHODS
  Crowded townships of Cape Town, South Africa, where human immunodeficiency virus (HIV) prevalence and tuberculosis (TB) notification rates are among the highest in the world.
  
  
  OBJECTIVE
  To determine age-specific prevalence rates of latent tuberculosis infection (LTBI) among HIV-negative individuals, and the annual risk and force of infection during childhood and adolescence.
  
  
  METHODS
  A cross-sectional survey using a standardised tuberculin skin test (TST) in HIV-negative individuals aged 5-40 years. A TST diameter of > or =10 mm was defined as indicative of LTBI.
  
  
  RESULTS
  Among 1061 individuals, only 4.7% had low-grade TST responses of 1-9 mm. However, the proportions of individuals with TST > or =10 mm increased from 28.0% in the 5-10 year age stratum to 88.0% in the 31-35 year age stratum. The mean annual risk of infection was 3.9% up to 5 years of age. The estimated force of infection (the rate of acquisition of LTBI among the residual pool of non-infected individuals) increased throughout childhood to a maximum of 7.9% per year at age 15 years.
  
  
  CONCLUSIONS
  Extremely high rates of infection in childhood and adolescence result in very high LTBI prevalence rates in young adults who are most at risk of acquiring HIV infection. This may be an important factor fuelling the high rates of HIV-associated TB in southern Africa.
authors.affiliation: Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: R
authors.initials: R
authors.lastname: Wood
authors.forename: H
authors.initials: H
authors.lastname: Liang
authors.forename: H
authors.initials: H
authors.lastname: Wu
authors.forename: K
authors.initials: K
authors.lastname: Middelkoop
authors.forename: T
authors.initials: T
authors.lastname: Oni
authors.forename: M X
authors.initials: MX
authors.lastname: Rangaka
authors.forename: R J
authors.initials: RJ
authors.lastname: Wilkinson
authors.forename: L-G
authors.initials: LG
authors.lastname: Bekker
authors.forename: S D
authors.initials: SD
authors.lastname: Lawn
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003906:Developing Countries / Q000706:statistics & numerical data*; D006306:Health Surveys; D006801:Humans; D055985:Latent Tuberculosis / Q000175:diagnosis / Q000453:epidemiology* / Q000635:transmission; D016015:Logistic Models; D011156:Population Density; D015995:Prevalence; D017678:Sex Distribution; D012737:Sex Factors; D013019:South Africa / Q000453:epidemiology; D013997:Time Factors; D014374:Tuberculin Test; D014505:Urban Population / Q000706:statistics & numerical data*; D055815:Young Adult