Tuberculosis contact screening and chemoprophylaxis

What it is

Contact screening asks whether a person in contact with a case of tuberculosis has been infected. Chemoprophylaxis is the drug course given to a contact in whom that infection is shown while the chest X-ray is normal.

Causes and risk

Almost all infections with M. tuberculosis are due to inhalation of droplet nuclei, 1 to 5 microns in diameter, which are infectious particles from a person with pulmonary tuberculosis aerosolized by coughing, sneezing or talking, and which dry while airborne and remain suspended for long periods. The air in a room occupied by a person with pulmonary tuberculosis may remain infectious for approximately 30 minutes even after that person has left it, and infection does not generally occur out of doors because M. tuberculosis is killed by ultraviolet light.

The most important determinants of infection of tuberculin-negative persons are closeness of contact and infectiousness of the source. Prolonged exposure and multiple aerosol inocula are usually required to establish the infection.