Cause
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; however, if they do cause disease, 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.
Geographical distribution
Worldwide. The risk of infection differs between countries, as shown on the map of estimated TB incidence.
Risk for travellers
Most travellers are at low risk for tuberculosis (TB). The risk for long-term travellers (>3 months) 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. Persons with HIV infection are at higher risk of TB.
Prophylaxis
BCG vaccine is of limited use for travellers but may be advised for infants and young children in some situations (see Chapter 6).
Precautions
Travellers should avoid close contact with known tuberculosis 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 in order to compare with retesting after return. If the skin reaction to tuber culin suggests recent infection, the traveller should receive, or be referred for, treatment for latent infection. Patients under treatment for tuberculosis should not travel until the treating physician has documented, by laboratory examination of sputum, that the patient is not infectious and therefore of no risk to others. The importance of completing the prescribed course of treatment should be stressed.
Vaccine
All versions of the BCG vaccine are based on live, attenuated mycobacterial strains descended from the original, attenuated bacillus Calmette-Guérin. The vaccine is administered intradermally and can be given simultaneously with other childhood vaccines. BCG vaccine is contraindicated for persons with severely impaired immunity, including individuals with HIV infection.
BCG vaccine is of very limited use for travellers. In the fi rst year of life it provides good protection against severe forms of TB (miliary TB and meningitis). In countries with high TB prevalence, infants are generally immunized with a single dose of BCG as soon after birth as possible. Children who are known to be HIVinfected, even if asymptomatic, should not be immunized with BCG vaccine.
Other protective benefi ts of the vaccine are uncertain. One dose of BCG should be considered for unvaccinated infants travelling from an area of low incidence to one of high incidence.
Many industrialized countries with a low incidence of TB have ceased giving BCG routinely to neonates.