title: Two-step tuberculin skin testing in school-going adolescents with initial 0-4 millimeter responses in a high tuberculosis prevalence setting in South India.
abstract: BACKGROUND
  The utility of two-step tuberculin skin testing among adolescents in high tuberculosis prevalence settings is not well established.
  
  
  OBJECTIVE
  To determine the proportion and determinants of a 0-4 mm response to an initial standard tuberculin skin test (TST) and evaluating 'boosting' with repeat testing.
  
  
  METHODS
  Adolescents between 11 and 18 years attending schools/colleges underwent a TST; those with a response of between 0-4 mm had a repeat TST 1-4 weeks later.
  
  
  RESULTS
  Initial TST was done for 6608/6643 participants; 1257 (19%) developed a 0-4 mm response to the initial TST. Younger age and under-nutrition were more likely to be associated with a 0-4 mm response, while the presence of BCG (Bacillus Calmette Guerin) scar and higher socio-economic class were less likely to be associated with a 0-4 mm response. On repeat testing boosting was seen in 13.2% (145/1098; ≥ 6 mm over the initial test) while 4.3% showed boosting using a more conservative cutoff of a repeat TST ≥ 10 mm with an increment of at least 6 mm (47/1098). History of exposure to a tuberculosis (TB) case was associated with enhanced response.
  
  
  CONCLUSIONS
  The proportion of adolescents who demonstrated boosting on two-step TST testing in our study was relatively low. As a result repeat testing did not greatly alter the prevalence of TST positivity. However, the two-step TST helps identify individuals who can potentially boost their immune response to a second test, and thus, prevents them from being misclassified as those with newly acquired infection, or tuberculin converters. While two-step tuberculin skin testing may have a limited role in population- level TST surveys, it may be useful where serial tuberculin testing needs to be performed to distinguish those who show an enhanced response or boosters from those who indeed have a new infection, or converters.
authors.affiliation: Department of Clinical Science, Infection, Faculty of Medicine and Dentistry, University of Bergen ; Department of Microbiology, Haukeland University Hospital, Bergen, Norway ; St. John's Research Institute, Bangalore, Karnataka, India.
authors.forename: Maitreyi
authors.initials: M
authors.lastname: Murthy
authors.forename: Sumithra
authors.initials: S
authors.lastname: Selvam
authors.forename: Nelson
authors.initials: N
authors.lastname: Jesuraj
authors.forename: Sean
authors.initials: S
authors.lastname: Bennett
authors.forename: Mark
authors.initials: M
authors.lastname: Doherty
authors.forename: Harleen M S
authors.initials: HM
authors.lastname: Grewal
authors.forename: Mario
authors.initials: M
authors.lastname: Vaz
mesh_terms: D000293:Adolescent; D001500:BCG Vaccine / Q000276:immunology; D002648:Child; D019353:Endemic Diseases; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D007194:India / Q000453:epidemiology; D008297:Male; D015995:Prevalence; D012867:Skin / Q000276:immunology; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D014611:Vaccination
chemical_list: D001500:BCG Vaccine
references.citation: Ann Intern Med. 1994 Feb 1;120(3):190-8
references.pmid: 8273982
references.citation: Clin Infect Dis. 1994 Jul;19(1):26-32
references.pmid: 7948554
references.citation: Int J Tuberc Lung Dis. 2004 Jul;8(7):842-7
references.pmid: 15260275
references.citation: Infect Control Hosp Epidemiol. 2004 Dec;25(12):1117-20
references.pmid: 15636304
references.citation: Int J Tuberc Lung Dis. 2008 Dec;12(12):1407-13
references.pmid: 19017450
references.citation: Pulm Med. 2013;2013:601737
references.pmid: 23476763
references.citation: Int J Tuberc Lung Dis. 2008 Dec;12(12):1401-6
references.pmid: 19017449
references.citation: Vaccine. 2005 Jun 10;23(30):3991-8
references.pmid: 15899539
references.citation: Ann Intern Med. 2007 Mar 6;146(5):340-54
references.pmid: 17339619
references.citation: Am J Respir Crit Care Med. 1999 Jan;159(1):15-21
references.pmid: 9872812
references.citation: Tuberculosis (Edinb). 2011 Dec;91 Suppl 1:S34-7
references.pmid: 22099419
references.citation: J Glob Infect Dis. 2011 Jan;3(1):94
references.pmid: 21572618
references.citation: Pediatrics. 2003 Oct;112(4):e298
references.pmid: 14523215
references.citation: Indian Pediatr. 1998 Jun;35(6):582-4
references.pmid: 10216667
references.citation: Pak J Biol Sci. 2008 Mar 15;11(6):930-3
references.pmid: 18814659
references.citation: PLoS One. 2009 Aug 24;4(8):e6686
references.pmid: 19701460
references.citation: S Afr Med J. 1990 Apr 21;77(8):387-9
references.pmid: 2330523
references.citation: Ann Intern Med. 2008 Aug 5;149(3):177-84
references.pmid: 18593687
references.citation: Int J Tuberc Lung Dis. 2010 Aug;14(8):952-9
references.pmid: 20626938
references.citation: Int J Epidemiol. 2006 Dec;35(6):1447-54
references.pmid: 17008360
references.citation: Am J Infect Control. 1995 Jun;23(3):181-7
references.pmid: 7677263
references.citation: Int J Tuberc Lung Dis. 2000 May;4(5):420-6
references.pmid: 10815735
references.citation: PLoS One. 2011 Apr 04;6(4):e18206
references.pmid: 21483746
references.citation: Bull World Health Organ. 1955;12(1-2):63-83
references.pmid: 14351968
references.citation: Bull World Health Organ. 1974;51(3):273-8
references.pmid: 4218969
references.citation: J Hosp Infect. 2000 Oct;46(2):141-6
references.pmid: 11049708
references.citation: Clin Microbiol Infect. 2004 Nov;10(11):980-3
references.pmid: 15522000