The infectiousness of a TB patient is directly related to the number of tubercle bacilli that he or she expels into the air. Patients who expel many tubercle bacilli are more infectious than patients who expel few or no bacilli. Patients are more likely to be infectious if they:
- Have TB of the lungs or larynx
- Have a cavity in the lung
- Are coughing or undergoing cough-inducing procedures
- Are not covering their mouth when coughing
- Have acid-fast bacilli on the sputum smear
- Are not receiving adequate treatment
Infectiousness appears to decline very rapidly after adequate treatment is started, but how quickly it declines varies from patient to patient. Patients who have been receiving adequate treatment for 2 to 3 weeks, whose symptoms have improved and who have 3 consecutive negative sputum smears from sputum collected on different days can usually be considered noninfectious.
TB can be spread in many places, such as homes or worksites. TB can also be transmitted in health care facilities. TB is most likely to be transmitted when health care workers and patients come in contact with patients who have unsuspected TB disease, who are not receiving adequate treatment, and who have not been isolated from others. All health care facilities should take measures to prevent the spread of TB. In other words, the dangerous case as far as transmission is concerned is the undiagnosed case.
The main goal of an infection control program is to detect TB disease early and to promptly isolate and treat people who have TB disease. The infection control program should involve three types of controls - administrative controls, engineering controls, and personal respiratory protection - as well as training and education and TB screening for health care workers.
Patients who have signs or symptoms of TB disease should be placed in an area away from other patients and promptly given a diagnostic evaluation. Patients who are likely to have TB should start appropriate treatment at once after appropriate confirmations specimens are collected. In hospitals and other inpatient settings, patients known to have TB disease or suspected of having TB disease should be placed in a special isolation room right away. This isolation room should be at negative pressure relative to other parts of the facility.
Three types of engineering controls are used to prevent the transmission of TB in health care facilities: ventilation, high-efficiency particulate air (HEPA) filtration, and ultraviolet germicidal irradiation (UVGI). HEPA filters and UVGI should be used in conjunction with other infection control measures.
In places where administrative and engineering controls may not fully protect health care workers from infectious droplet nuclei, health care workers should use personal respirators to filter out droplet nuclei.
The health department should work closely with health care facilities to:
- Help them report confirmed or suspected TB cases as quickly as possible
- Conduct contact investigations
- Make sure there is a plan for TB patients to receive follow-up care after they are discharged
- Help the facilities with screening, surveillance, outbreak investigations, and other aspects of a TB infection control program
People with TB disease are most likely to transmit TB before the disease has been diagnosed and treatment has started. TB patients who are receiving treatment are less likely to be infectious. TB patients who may be infectious should be instructed to cover their mouth and nose with a tissue when coughing or sneezing.
Health care workers who visit TB patients at home should take precautions to protect themselves from the spread of TB. They should instruct patients to cover their mouth and nose with a tissue when coughing or sneezing, wear a personal respirator when visiting the home of an infectious TB patient or when transporting an infectious TB patient in a vehicle, collect sputum specimens in a well-ventilated area (if possible outdoors), and participate in a TB screening and prevention program.