Isolation and de-isolation of the patient with infectious tuberculosis

What it is

Almost all infections with M. tuberculosis are due to inhalation of droplet nuclei of 1-5 microns, infectious particles from a person with pulmonary tuberculosis aerosolized by coughing, sneezing or talking, which dry while airborne and remain suspended for long periods. The air in a room occupied by such a person may remain infectious for approximately 30 minutes even after his or her absence. Because the route is the air, tuberculosis is placed under airborne precautions, in a negative pressure room. That box holds two lists: chicken pox, disseminated herpes zoster, that is shingles, and measles in the first; and under N-95 mask, tuberculosis, SARS and avian influenza in the second.

Causes and risk

The factors associated with increased risk of transmission fall into four groups.

• Patient factors: respiratory disease, pulmonary or laryngeal; the number of patients with respiratory TB disease; respiratory secretions that are acid-fast bacteria smear positive; presence of cough; HIV infection; and atypical manifestations of disease.
• Diagnostic and laboratory factors: cough-inducing procedures such as sputum induction, bronchoscopy or administration of aerosolized therapies; delayed diagnosis; autopsy and preparation of pathology specimens; and improper handling of laboratory specimens containing M. tuberculosis.
• Treatment factors: incorrect, ineffective or no therapy, and delayed treatment.
• Environmental factors: inadequate ventilation to remove airborne infectious M. tuberculosis; inadequate TB infection prevention and control measures; duration of exposure and proximity to the infectious patient; overcrowding; absence of sunlight; and high humidity.

Infection does not generally occur out of doors because M. tuberculosis is killed by ultraviolet light. Prolonged exposure and multiple aerosol inocula are usually required to establish the infection, and the most important determinants of infection of tuberculin-negative persons are closeness of contact and infectiousness of the source.