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Molecular epidemiology unmasks the tubercle bacillus: new techniques reveal new aspects of virulence
  1. P D O Davies
  1. Correspondence to:
    P D O Davies
    Cardiothoracic Centre, Thomas Drive, Liverpool L14 3PE;

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Molecular methods show that TB is being transmitted with surprising efficiency

Two papers in this month’s edition of Thorax show how the use of strain typing of Mycobacterium tuberculosis can reveal new aspects of tuberculosis (TB) transmission.1,2 The study by Ruddy et al,1 based around an outbreak of isoniazid resistant TB in north London, shows that a single outbreak can extend over many years and affect a broad range of individuals including medical staff. The second study by Hernández-Garduño et al2 suggests that sputum smear negative disease can have an appreciable transmission rate. Although molecular epidemiology can unmask the problem, solutions may be more difficult to develop.


Using IS6110 restriction fragment length polymorphism (RFLP) analysis, at the time of writing Ruddy et al had identified over 70 cases, ominously adding that, on epidemiological modelling, the peak had not yet been reached. Initial estimates by the end of December 2003 suggest that the outbreak may already have reached 132 (Dr Helen Maguire, personal communication).

This is the biggest outbreak ever identified in the UK, although not from a single point source, as was the more spectacular Leicester outbreak.3 The outbreak of isoniazid resistant TB in north London reported by Ruddy and colleagues seems to have been largely among groups of young adults of mixed ethnic backgrounds, particularly black Caribbean and white, although some were of business or professional backgrounds. Drug misuse and/or prison detention were common to many cases. Although the association between prison and TB has been well established in countries such as Russia and the USA,4,5 this is the first prison outbreak to be documented in the UK. We have previously been quite proud of our record of …

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