The Northern Territory Disease Control Bulletin
Territory Health Services, Centre for Disease Control
Northern Territory disease control bulletin; E-Journals; PublicationNT; Northern Territory disease control bulletin
Date:2002-03; This publication contains may contain links to external sites. These external sites may no longer be active.; Made available via the Publications (Legal Deposit) Act 2004 (NT).
Communicable diseases; Reporting; Northern Territory; Statistics; Periodicals
Northern Territory Government
Northern Territory disease control bulletin
v. 9 no. 1
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
The Northern Territory Disease Control Bulletin Vol 9, No.1, March 2002 9 non-Aboriginal Australian born students to those living in Aboriginal communities has had an effect with the proportion of Mantoux positive students increasing from 3.9% prior to 1997 to 5.0% thereafter. The numbers screened per year fell from an average of 2,060 per year (1991-96) to 608 per year (1997-2000). However the review has shown that focussing on the more at risk group for screening after 1996 has not necessarily resulted in improved coverage as envisioned. The Mantoux positivity of the overseas born students likely reflects the infection rate in the countries in which they were born rather than that of the community in which they now live and remained higher than that of the Aboriginal students throughout the 10 years of screening. Furthermore, screening programs in southern states have revealed Mantoux positivity rates in overseas born children much higher than those recorded in the NT (up to 27%2). The reason for this is unclear but may reflect to different mix of immigrants in other cities. A study from Melbourne showed 0% prevalence in those from southern Europe to a prevalence of 15.9% for those from Indo China.3 Patterns of the Mantoux response across the target groups reflect the underlying exposure to mycobacterial antigens of that population. Populations with a greater degree of exposure to M. tuberculosis will have a greater proportion of Mantoux responses in the 10-15 mm range and this will be seen as a second rise in the curve describing the distribution of Mantoux size. Hence, it can be seen that Australian born nonAboriginal students have a pattern which reflects minimal exposure to M. tuberculosis, while overseas born and Aboriginal students have an obvious biphasic pattern reflecting a greater degree of exposure. This reinforces the maxim that tuberculin testing needs to be interpreted with the underlying risk of TB exposure in mind. Outcome measures for 2000 revealed that a disappointing number of students (17.6% of those reviewed and eligible) completed the six month course of isoniazid. Given that treatment of LTBI is the major clinical benefit of the program, unless the number of completed courses can be increased, continuing the program would be difficult to justify. From a monetary viewpoint, cost benefit analysis has revealed that Mantoux school screening programs become cost saving in student populations when the Mantoux positivity rate reaches 20%4, which is significantly more than the rates observed in this program. While costbenefit status ought not to be the sole determinant of a programs existence, it does give a benchmark of efficiency and allows comparisons to be made with other health interventions. The NT TB guidelines are currently under revision and while this is happening school screening will continue for 2002. It will be important to demonstrate an ability to adequately screen the at-risk group of students as per the 1997 policy change and to achieve positive clinical outcomes in the future or the place of school screening as a useful disease prevention strategy (ie for identifying and treating LTBI) is in doubt. References 1. Wright J. and Krause V. Outcomes of NT School Mantoux Program 1991-1994. Abstract:PHA 2nd National Tuberculosis Conference, Sydney, 17-18 November 1997. 2. Alperstein J, Fett MJ, Reznik R, Thomas M, Senthil M. The prevalence of tuberculosis infection among Year 8 schoolchildren in inner Sydney in 1992. Med J Aust 1994;160:197-201. 3. Johnson PD, Carlin JB, Bennett CM, et al. Prevalence of tuberculosis infection in Melbourne secondary school students. Med J Aust 1998;168 (3):100-101. 4. Mohle-Boetani JC, Miller B, Halpern M, Trivedi A, Lessler J, Solomon S, Fenstersheib M. Schoolbased screening for tuberculosis infection. A costbenefit analysis. JAMA 1995;274:613-619. *************
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