title: The prevalence of latent Mycobacterium tuberculosis infection based on an interferon-γ release assay: a cross-sectional survey among urban adults in Mwanza, Tanzania.
abstract: BACKGROUND
  One third of the world's population is estimated to be latently infected with Mycobacterium tuberculosis (LTBI). Surveys of LTBI are rarely performed in resource poor TB high endemic countries like Tanzania although low-income countries harbor the largest burden of the worlds LTBI. The primary objective was to estimate the prevalence of LTBI in household contacts of pulmonary TB cases and a group of apparently healthy neighborhood controls in an urban setting of such a country. Secondly we assessed potential impact of LTBI on inflammation by quantitating circulating levels of an acute phase reactant: alpha-1-acid glycoprotein (AGP) in neighborhood controls.
  
  
  METHODS
  The study was nested within the framework of two nutrition studies among TB patients in Mwanza, Tanzania. Household contacts- and neighborhood controls were invited to participate. The study involved a questionnaire, BMI determination and blood samples to measure AGP, HIV testing and a Quantiferon Gold In tube (QFN-IT) test to detect signs of LTBI.
  
  
  RESULTS
  245 household contacts and 192 neighborhood controls had available QFN-IT data. Among household contacts, the proportion of QFT-IT positive was 59% compared to 41% in the neighborhood controls (p = 0.001). In a linear regression model adjusted for sex, age, CD4 and HIV, a QFT-IT positive test was associated with a 10% higher level of alpha-1-acid glycoprotein(AGP) (10(B) 1.10, 95% CI 1.01; 1.20, p = 0.03), compared to individuals with a QFT-IT negative test.
  
  
  CONCLUSIONS
  LTBI is highly prevalent among apparently healthy urban Tanzanians even without known exposure to TB in the household. LTBI was found to be associated with elevated levels of AGP. The implications of this observation merit further studies.
authors.affiliation: Department of Infectious Diseases, Odense University Hospital, Odense, Denmark.
authors.forename: Andreas V
authors.initials: AV
authors.lastname: Jensen
authors.forename: Lotte
authors.initials: L
authors.lastname: Jensen
authors.forename: Daniel
authors.initials: D
authors.lastname: Faurholt-Jepsen
authors.forename: Martine G
authors.initials: MG
authors.lastname: Aabye
authors.forename: George
authors.initials: G
authors.lastname: Praygod
authors.forename: Jeremiah
authors.initials: J
authors.lastname: Kidola
authors.forename: Maria
authors.initials: M
authors.lastname: Faurholt-Jepsen
authors.forename: John
authors.initials: J
authors.lastname: Changalucha
authors.forename: Nyagosya
authors.initials: N
authors.lastname: Range
authors.forename: Henrik
authors.initials: H
authors.lastname: Krarup
authors.forename: Henrik
authors.initials: H
authors.lastname: Friis
authors.forename: Aase B
authors.initials: AB
authors.lastname: Andersen
mesh_terms: D000328:Adult; D060085:Coinfection / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D015658:HIV Infections / Q000453:epidemiology; D006801:Humans; D059425:Interferon-gamma Release Tests; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D013636:Tanzania / Q000453:epidemiology; D014505:Urban Population; D055815:Young Adult