Molecular epidemiology unmasks the tubercle bacillus: new techniques reveal new aspects of virulence.

The article shows how the use of strain typing of Mycobacterium tuberculosis can reveal new aspects of tuberculosis (TB) transmission. The study by M.C. Ruddy and colleagues, 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-Gardu&nmacr;o and others 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. Molecular methods show that TB is being transmitted with surprising efficiency.