Mycobacterium tuberculosis, the tubercle bacillus.
Infection is usually by direct airborne transmission from person to person.
Nature of the disease
Exposure to M. tuberculosis may lead to infection, but most infections do not lead to disease. The risk of developing disease following infection is generally 5–10% during the lifetime but may be increased by various factors, notably immunosuppression (e.g. advanced HIV infection). Multidrug resistance refers to strains of M. tuberculosis that are resistant to at least isoniazid and rifampicin (MDR-TB). The resistant strains do not differ from other strains in infectiousness, likelihood of causing disease, or general clinical effects; if they do cause disease, however, treatment is more difficult and the risk of death will be higher. Extensively drug-resistant TB (XDR-TB) is TB that is resistant to at least isoniazid and rifampin, to any fluoroquinolone and to at least one of the injectable second-line anti-TB drugs capreomycin, kanamycin and amikacin.
Worldwide. The risk of infection differs between countries, as shown on the map of estimated tuberculosis incidence.
Risk for travellers
Most travellers are at low risk for TB. The risk for long-term (over 3 months) travellers in a country with a higher incidence of TB than their own may be comparable to the risk for local residents. Living conditions, as well as duration of travel and purpose of travel, e.g. emergency relief, are important in determining the risk of infection: high-risk settings include impoverished communities, areas experiencing civil unrest or war, refugee areas, health facilities, prisons and shelters for the homeless. Individuals with HIV infection are at higher risk of TB.
Travellers should avoid close contact with known TB patients. For travellers from low-incidence countries who may be exposed to infection in relatively high-incidence countries (e.g. health professionals, humanitarian relief workers, missionaries), a baseline tuberculin skin test is advisable for comparison with retesting after return. If the skin reaction to tuberculin suggests recent infection, the traveller should receive, or be referred for, treatment for latent infection. Patients under treatment for TB should not travel until the treating physician has documented, by laboratory examination of sputum, that they are not infectious and are therefore of no risk to others. The importance of completing the prescribed course of treatment should be stressed.