Transmission

Only people with active pulmonary or laryngeal tuberculosis are infectious to other people. People who have latent or extrapulmonary tuberculosis are not infectious. M. tuberculosis is transmitted through the air, usually when someone with active tuberculosis coughs, sneezes, shouts or talks.  People who are being treated for active tuberculosis remain infectious until confirmed otherwise: see Treating active tuberculosis below.

In the United Kingdom and the United States, there have been cases in which people have become infected in hospitals due to inadequate infection control procedures. People who are suspected of having active tuberculosis should be nursed in single rooms with negative air pressure, meaning that air is gently sucked out of the room so that any organisms cannot escape into the rest of the hospital.

Exposure to TB in healthcare settings is a particular risk for HIV-positive people because of the high existing rates of HIV/TB coinfection in resource-limited settings. Ventilating tuberculosis (TB) wards by opening windows is more likely to reduce the risk of infection than mechanical ventilation and should be practiced wherever the climate permits.¹

It is important to avoid contact with people who have active lung tuberculosis until they are no longer infectious. If an HIV-positive person is exposed to someone with tuberculosis, they should see their doctor as soon as possible.