title: A threshold value for the time delay to TB diagnosis.
abstract: BACKGROUND
  In many communities where TB occurs at high incidence, the major force driving the epidemic is transmission. It is plausible that the typical long delay from the onset of infectious disease to diagnosis and commencement of treatment is almost certainly the major factor contributing to the high rate of transmission.
  
  
  RESULTS
  This study is confined to communities which are epidemiologically relatively isolated and which have low HIV incidence. The consequences of delays to diagnosis are analyzed and the existence of a threshold delay value is demonstrated. It is shown that unless a sufficient number of cases are detected before this threshold, the epidemic will escalate. The method used for the analysis avoids the standard computer integration of systems of differential equations since the intention is to present a line of reasoning that reveals the essential dynamics of an epidemic in an intuitively clear way that is nevertheless quantitatively realistic.
  
  
  CONCLUSIONS
  The analysis presented here shows that typical delays to diagnosis present a major obstacle to the control of a TB epidemic. Control can be achieved by optimizing the rapid identification of TB cases together with measures to increase the threshold value. A calculated and aggressive program is therefore necessary in order to bring about a reduction in the prevalence of TB in a community by decreasing the time to diagnosis in all its ramifications. Intervention strategies to increase the threshold value relative to the time to diagnosis and which thereby decrease disease incidence are discussed.
authors: Division of Molecular Biology and Human Genetics, MRC Center for Molecular and Cellular Biology, Faculty of Health Sciences, Stellenbosch University, Cape Town, Western Cape, Republic of South Africa.
authors: Pieter W
authors: PW
authors: Uys
authors: Robin M
authors: RM
authors: Warren
authors: Paul D
authors: PD
authors: van Helden
mesh_terms: D004198:Disease Susceptibility; D015658:HIV Infections / Q000453:epidemiology; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000472:pathogenicity; D013019:South Africa / Q000453:epidemiology; D013997:Time Factors; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000453:epidemiology* / Q000635:transmission
references: J Microbiol Methods. 2001 May;45(1):41-52
references: 11295196
references: Int J Tuberc Lung Dis. 2006 Jan;10(1):24-30
references: 16466033
references: J Clin Microbiol. 1986 May;23(5):822-5
references: 3086369
references: Lancet. 1983 Sep 17;2(8351):651-2
references: 6136798
references: Am J Respir Crit Care Med. 2000 Dec;162(6):2033-8
references: 11112109
references: J Clin Microbiol. 1992 Sep;30(9):2415-8
references: 1401008
references: J Theor Biol. 2000 Oct 7;206(3):327-41
references: 10988019
references: JAMA. 2002 Feb 27;287(8):996-1002
references: 11866647
references: Pediatrics. 2004 Jun;113(6):e514-9
references: 15173530
references: Scand J Infect Dis. 2001;33(4):279-84
references: 11345220
references: Trans R Soc Trop Med Hyg. 2005 Dec;99(12):893-900
references: 16139316
references: Am J Respir Crit Care Med. 1998 Apr;157(4 Pt 1):1244-8
references: 9563746
references: JAMA. 2002 Feb 27;287(8):991-5
references: 11866646
references: Kekkaku. 1994 May;69(5):375-7
references: 8007524
references: Annu Rev Public Health. 2004;25:303-26
references: 15015922
references: Int J Epidemiol. 2004 Apr;33(2):351-7
references: 15082639
references: Int J Tuberc Lung Dis. 1999 Dec;3(12):1088-95
references: 10599012
references: Int J Tuberc Lung Dis. 2000 Feb;4(2):133-8
references: 10694091
references: J Clin Microbiol. 2000 Jun;38(6):2278-83
references: 10834989
references: J Infect Dis. 2007 Aug 15;196 Suppl 1:S15-27
references: 17624822