The Editorial Executive Committee welcomes letters, which should be less than 250 words. Before a decision to publish is made, letters which refer to a published article may be sent to the author for a response. Any letter may be sent to an expert for comment. When letters are published, they are usually accompanied in the same issue by their responses or comments. The Committee screens out discourteous, inaccurate or libellous statements. The letters are sub-edited before publication. Authors are required to declare any conflicts of interest. The Committee's decision on publication is final.

Letter to the editor

Editor, – In their articles on BCG vaccination (Aust Prescr 2003;26:144-6), neither Professor Simpson nor Air Vice-Marshal Short mentioned the potential for tuberculosis control offered by modern tuberculosis-specific tests that are unaffected by BCG vaccination. T-cell mediated immune responses to the tuberculosis-specific proteins ESAT-6 and CFP-10 (proteins not present in BCG or environmental mycobacteria) have been shown to be effective in diagnosing tuberculosis infection in BCG-vaccinated individuals.1,2

Unfortunately, despite intense interest in the literature, the use of tuberculosis-specific antigens in diagnostics has to date been limited by the complexity of the methodologies required to measure T-cell responses. Most methods require T-cell purification, counting, and culture, which are expensive and not suited for reproducible, robust diagnosis. However, the whole blood test, QuantiFERON-TB Gold, has now been released in Australia, after extensive testing overseas found it to have high specificity and sensitivity.

The Australian Defence Force may also note the US Centers for Disease Control endorses QuantiFERON-TB testing in the military.3 QuantiFERON testing detects significantly more active, infectious tuberculosis cases than Mantoux testing.4 The elimination of the confounding factors of BCG vaccination and sensitisation to non-tuberculous mycobacteria makes the test an even more valuable diagnostic tool.

Tony Radford
Chief Executive Officer/Managing Director
Cellestis Ltd.
Melbourne

(Cellestis are manufacturers of QuantiFERON products)

Author's comments

Professor G. Simpson, the author of the article, comments:

I did not discuss some of the newer tests for the diagnosis of latent tuberculous infection as the focus of the article was BCG. The tuberculin skin test (TST) or Mantoux test was mentioned as it is the test specified in current protocols concerned with BCG administration. Dr Radford is correct that the TST is imperfect and there is no doubt that sooner or later more sophisticated tests will replace it. Over the past 110 years however, it has proved remarkably robust and we do have vast amounts of data on outcomes related to TST results. These longitudinal data are not available for the newer tests.

The newer tests (QuantiFERON-TB Gold and ELISPOT) rely on detecting interferon gamma production by T-cells responding to antigens which are found in M tuberculosis, but not in BCG. This theoretically will enable us to remove the confounding effect of prior BCG vaccination from testing for subsequent tuberculosis infection. This is of course irrelevant in the context of pre-BCG vaccination testing. So far there is more published information on ELISPOT than QuantiFERON-TB Gold. In the best study so far5 in a tuberculosis outbreak in the UK the ELISPOT and Heaf test (a form of TST) gave concordant results in 89% of those tested, suggesting that there is limited room for improved diagnostic accuracy with the newer tests. Nevertheless these are exciting developments in tuberculosis diagnosis and further studies including more longitudinal studies are likely to sound the death knell for the oldest diagnostic test in medicine.

Letter to the editor

Editor, – I noted with interest the photo illustrating the article 'BCG vaccine in Australia' (Aust Prescr 2003;26:144-6). What has happened to universal infection control precautions - surely the person administering the injection should have been wearing gloves?

Anna McNulty
Director
Sydney Sexual Health Centre

References

  1. Andersen P, Munk ME, Pollock JM, Doherty TM. Specific immune-based diagnosis of tuberculosis. Lancet 2000;356:1099-104.
  2. Doherty TM, Demissie A, Olobo J, Wolday D, Britton S, Eguale T, et al. Immune responses to the Mycobacterium tuberculosis-specific antigen ESAT-6 signal subclinical infection among contacts of tuberculosis patients. J Clin Microbiol 2002;40:704-6.
  3. Mazurek GH, Villarino ME. Guidelines for using the QuantiFERON(R)-TB test for diagnosing latent Mycobacterium tuberculosis infection. Centers for Disease Control and Prevention. MMWR 2003 Jan 31;52(RR-2):15-8.
  4. Fietta A, Meloni F, Cascina A, Morosini M, Marena C, Troupioti P, et al. Comparison of a whole-blood interferon-gamma assay and tuberculin skin testing in patients with active tuberculosis and individuals at high or low risk of Mycobacterium tuberculosis infection. Am J Infect Control 2003;31:347-53.
  5. Ewer K, Deeks J, Alvarez L, Bryant G, Waller S, Andersen P, et al. Comparison of T-cell-based assay with tuberculin skin test for diagnosis of Mycobacterium tuberculosis infection in a school tuberculosis outbreak. Lancet 2003;361:1168-73.