title: Epidemiologic inference from the distribution of tuberculosis cases in households in Lima, Peru.
abstract: BACKGROUND
  Tuberculosis (TB) often occurs among household contacts of people with active TB. It is unclear whether clustering of cases represents household transmission or shared household risk factors for TB.
  
  
  METHODS
  We used cross-sectional data from 764 households in Lima, Peru, to estimate the relative contributions of household and community transmission, the average time between cases, and the immunity afforded by a previous TB infection.
  
  
  RESULTS
  The distribution of cases per household suggests that almost 7 of 10 nonindex household cases were infected in the community rather than in the household. The average interval between household cases was 3.5 years. We observed a saturation effect in the number of cases per household and estimated that protective immunity conferred up to 35% reduction in the risk of disease.
  
  
  CONCLUSIONS
  Cross-sectional household data can elucidate the natural history and transmission dynamics of TB. In this high-incidence setting, we found that the majority of cases were attributable to community transmission and that household contacts of case patients derive some immunity from household exposures. Screening of household contacts may be an effective method of detecting new TB cases if carried out over several years.
authors: Department of Epidemiology, Harvard School of Public Health, Brigham and Women's Hospital, Massachusetts General Hospital, Boston, USA. ellen.brooks.pollock@gmail.com
authors: Ellen
authors: E
authors: Brooks-Pollock
authors: Mercedes C
authors: MC
authors: Becerra
authors: Edward
authors: E
authors: Goldstein
authors: Ted
authors: T
authors: Cohen
authors: Megan B
authors: MB
authors: Murray
references: JAMA. 1994 Mar 2;271(9):698-702
references: 8309034
references: Am Rev Tuberc. 1952 Feb;65(2):111-27
references: 14885714
references: Am J Epidemiol. 2003 Dec 1;158(11):1039-47
references: 14630599
references: PLoS Negl Trop Dis. 2009;3(3):e401
references: 19333364
references: Am J Respir Crit Care Med. 2003 Aug 15;168(4):448-55
references: 12773322
references: Am J Public Health Nations Health. 1933 May;23(5):426-32
references: 18013728
references: Epidemiol Infect. 2004 Jun;132(3):433-41
references: 15188713
references: Lancet. 2011 Jan 8;377(9760):147-52
references: 21145581
references: Epidemiol Rev. 2001;23(2):288-301
references: 12192738
references: Stat Med. 2004 Nov 30;23(22):3469-87
references: 15505892
references: Lancet. 1995 Feb 18;345(8947):416-9
references: 7853950
references: Am J Epidemiol. 1982 May;115(5):736-51
references: 7081204
references: Int J Tuberc Lung Dis. 2003 May;7(5):426-31
references: 12757042
references: J Infect Dis. 2002 Feb 1;185(3):401-4
references: 11807725
references: Biometrics. 1982 Mar;38(1):115-26
references: 7082755
references: Bull Int Union Tuberc. 1972 Feb;47:116-34
references: 5077111
references: Epidemiol Infect. 1997 Oct;119(2):183-201
references: 9363017
references: Int J Tuberc Lung Dis. 1999 May;3(5):414-20
references: 10331731
references: Lancet Infect Dis. 2008 Jun;8(6):359-68
references: 18450516
references: Lancet. 2004 Jan 17;363(9404):212-4
references: 14738796
references: Epidemiol Infect. 2007 Jan;135(1):27-33
references: 16740189
references: Respir Med. 1991 Nov;85(6):475-7
references: 1775674
references: Int J Tuberc Lung Dis. 2001 Apr;5(4):321-8
references: 11334250
references: Int J Tuberc Lung Dis. 2002 Mar;6(3):266-9
references: 11934145
references: N Engl J Med. 2003 Jan 9;348(2):119-28
references: 12519922
references: Am J Epidemiol. 2000 Aug 1;152(3):247-63
references: 10933272
references: Tubercle. 1983 Dec;64(4):241-53
references: 6606884
references: Int J Tuberc Lung Dis. 2003 Dec;7(12 Suppl 3):S501-9
references: 14677844
references: Infect Immun. 2001 Jul;69(7):4195-201
references: 11401954
references: Nat Med. 1995 Aug;1(8):815-21
references: 7585186
references: Am J Epidemiol. 2003 Nov 1;158(9):887-98
references: 14585767
references: N Engl J Med. 1999 Oct 14;341(16):1174-9
references: 10519895
references: Arch Bronconeumol. 2007 Jun;43(6):317-23
references: 17583641
references: JAMA. 1999 Aug 18;282(7):677-86
references: 10517722
references: Br Med J. 1967 Mar 11;1(5540):587-92
references: 6023319
references: Tuberculosis (Edinb). 2009 Mar;89(2):120-5
references: 19054717