title: Methodological issues in quantifying the magnitude of the tuberculosis problem in a prison population.
abstract: METHODS
  Correctional settings and remand prisons.
  
  
  OBJECTIVE
  To critically discuss calculations for epidemiological indicators of the tuberculosis (TB) burden in prisons and to provide recommendations to improve study comparability.
  
  
  METHODS
  A hypothetical data set illustrates issues in determining incidence and prevalence. The appropriate calculation of the incidence rate is presented and problems arising from cross-sectional surveys are clarified.
  
  
  RESULTS
  Cases recognized during the first 3 months should be classified as prevalent at entry and excluded from any incidence rate calculation. The numerator for the incidence rate includes persons detected as having developed TB during a specified period of time subsequent to the initial 3 months. The denominator is person-time at risk from 3 months onward to the end point (TB or end of the observation period). Preferably, entry time, exit time and event time are known for each inmate to determine person-time at risk. Failing that, an approximation consists of the sum of monthly head counts, excluding prevalent cases and those persons no longer at risk from both the numerator and the denominator.
  
  
  CONCLUSIONS
  The varying durations of inmate incarceration in prisons pose challenges for quantifying the magnitude of the TB problem in the inmate population. Recommendations are made to measure incidence and prevalence.
authors.affiliation: International Union Against Tuberculosis and Lung Disease, Paris, France. TBRieder@tbrieder.org
authors.forename: H L
authors.initials: HL
authors.lastname: Rieder
authors.forename: C
authors.initials: C
authors.lastname: Anderson
authors.forename: M
authors.initials: M
authors.lastname: Dara
authors.forename: B
authors.initials: B
authors.lastname: Hauer
authors.forename: P
authors.initials: P
authors.lastname: Helbling
authors.forename: K M
authors.initials: KM
authors.lastname: Kam
authors.forename: M
authors.initials: M
authors.lastname: Zwahlen
mesh_terms: D003430:Cross-Sectional Studies; D015340:Epidemiologic Research Design; D006801:Humans; D015994:Incidence; D015995:Prevalence; D011329:Prisoners / Q000706:statistics & numerical data*; D012306:Risk; D013997:Time Factors; D014376:Tuberculosis / Q000453:epidemiology*