The emergence of MDdR-TB and extensively drug-resistant TB (XDdR-TB) has raised special concerns in relation to the international spread of particularly dangerous strains of Mycobacterium tuberculosis. Since the 2006 edition was published, several incidents have occurred involving air travel and potential transmission of TB. The revision of the International Health Regulations (IHR), which entered into force in June 2007, provides for the introduction of new measures that might potentially apply to international events involving TB. The IHR provide a legal framework for a more effective and co