Tuberculosis

Click on a flag to turn the WHOLE website into the language of your choice

PLEASE NOTE THIS SITE IS MOVING TO A NEW ADDRESS TB and U FREEHOSTIA
PLEASE BOOKMARK AS THIS ADDRESS WILL NOT BE AVAILABLE AFTER 22ND JULY 2008

Transmission 1

The infectious agent of tuberculosis, Mycobacterium tuberculosis, is carried on airborne droplet nuclei. Droplet nuclei are produced when persons with pulmonary tuberculosis cough, sneeze, speak, or sing. They also may be produced through manipulation of lesions or processing of tissue or secretions in the hospital or laboratory. Droplet nuclei are so small (1 to 5 um) that air currents normally present in any indoor space can keep them airborne for long periods of time. Once released from the host, they are dispersed throughout the room.

Although patients with tuberculosis also generate larger particles containing numerous bacilli, these particles do not serve as effective vehicles for transmission of infection because they do not remain airborne, and if inhaled, do not reach alveoli. Organisms deposited on intact mucosa or skin do not invade tissue. When large particles are inhaled, they impact on the wall of the upper airway or trachea, where they are trapped in the mucous blanket, carried to the oropharynx, and swallowed or expectorated.

Transmission 2

Techniques that reduce the number of droplet nuclei in the room air are effective in preventing the airborne transmission of tuberculosis. Ventilation with fresh air is especially important, with six or more room-air changes an hour being desirable. The number of viable airborne tubercle bacilli can be reduced by ultraviolet irradiation of air in the upper part of the room.

Effective antituberculosis chemotherapy reduces the number of bacilli released into the air by reducing the number of organisms in the sputum and the frequency of coughing. Covering the mouth and the nose with tissues while coughing or sneezing, or more effectively with a mask, reduces the number of organisms by reducing the number of droplet nuclei put into the air. If masks are to be used, they should be fabricated to filter out droplet nuclei and molded to fit tightly around the nose and mouth. Methods once thought to be important in preventing the transmission of tuberculosis -- disposing of such personal items as clothes and bedding, sterilizing fomites, using caps and gowns and gauze or paper masks, boiling dishes, and washing walls -- are unnecessary because they have no bearing on airborne transmission.

M. bovis may penetrate the gastrointestinal mucosa or invade the lymphatic tissue of the oropharynx when ingested in milk containing large numbers of organisms. Human infection with M. bovis has essentially been eliminated in developed countries as a result of the pasteurization of milk and effective tuberculosis control programs for cattle. Airborne transmission of M. bovis can also occur. 

Atypical TB