title: Prevalence and annual risk of tuberculosis infection in Laos.
abstract: METHODS
  Laos, where the implementation of a national tuberculosis program started in 1995.
  
  
  OBJECTIVE
  To estimate the prevalence (P) and annual risk of tuberculosis infection (ARTI) and relate this to case rates in the tuberculosis program.
  
  
  METHODS
  Tuberculin survey in schools in Vientiane municipality and three provinces. Sampling was not representative, but included schools in accessible districts in provinces with different characteristics. A group of 150 tuberculosis patients were tested for comparison.
  
  
  RESULTS
  An intra-dermal tuberculin test (PPD RT23/ Tween80) was applied to 11237 children; 9968 reactions were read, 4035 among first and second grade children with no BCG scar: 818 in Vientiane (mean age 8.4), 803 in Savannakhet (8.9), 1563 in Xiengkhuang (8.4), and 851 in Luangprabang (7.9). If reactions of > or =10 mm are counted, ARTI is estimated as 1.1% for the areas included in the survey with a strong variation by province (Vientiane 1.3%; Savannakhet 1.4%; Luangprabang 0.6%; Xiengkhuang 0.1%). The difference in ARTI is in accordance with differences in reported case rates in the provinces. The ARTI varied from 0.5% to 1.2%, depending on the method used for calculating P (Vientiane 0.6%-1.4%; Savannakhet 0.5-1.5%; Xiengkhuang 0.1%-0.2%; Luangprabang 0.4%-0.9%).
  
  
  CONCLUSIONS
  The ARTI is unequally distributed geographically and/or by ethnic group. It is generally higher in south and lower in central and north Laos. Improved methods are needed for estimating the prevalence of infection.
authors.affiliation: International Union Against Tuberculosis and Lung Disease, Paris, France. ruri@centrum.is
authors.forename: T H
authors.initials: TH
authors.lastname: Arnadottir
authors.forename: H
authors.initials: H
authors.lastname: Soukaseum
authors.forename: P
authors.initials: P
authors.lastname: Vangvichit
authors.forename: S
authors.initials: S
authors.lastname: Bounmala
authors.forename: E
authors.initials: E
authors.lastname: Vos
mesh_terms: D002648:Child; D002662:Child Health Services / Q000458:organization & administration*; D003150:Community Health Workers / Q000193:education; D005260:Female; D006801:Humans; D007812:Laos / Q000453:epidemiology; D008297:Male; D008403:Mass Screening / Q000458:organization & administration*; D015588:Observer Variation; D015995:Prevalence; D012306:Risk; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D014374:Tuberculin Test; D014376:Tuberculosis / Q000453:epidemiology* / Q000517:prevention & control