Tuberculosis (TB) is a contagious disease primarily caused by the bacterium Mycobacterium tuberculosis that most often targets the lungs. The infection spreads when a person with active disease coughs, sneezes, or talks, releasing bacteria into the air. Because these bacteria can remain suspended and infectious for extended periods, the primary infection control measure required for patients with active or suspected TB is Airborne Precautions. These precautions prevent microscopic particles containing the bacteria from circulating to other patients, visitors, and healthcare staff.
Understanding Airborne Transmission
Airborne Precautions are necessary because of the physical nature of the infectious particles. When a person with active pulmonary TB coughs or sneezes, they expel tiny, moisture-laden particles that dry out to form droplet nuclei, the mechanism of TB transmission.
Droplet nuclei are small, typically measuring between 1 and 5 micrometers (µm) in diameter. Due to their minute size, they are not subject to the rapid gravitational pull that affects larger respiratory droplets. Instead, droplet nuclei remain suspended in the air for hours and can be carried on air currents throughout a room or building.
This ability to linger and travel long distances differentiates airborne spread from droplet spread, which only occurs within a short range. Activities like coughing, talking, and even breathing aerosolize these infectious particles, making containment measures mandatory.
Implementing Airborne Isolation
Airborne Precautions involve specialized environmental controls and personal protective equipment (PPE). Patients suspected of having infectious TB are immediately placed in an Airborne Infection Isolation Room (AIIR), which features a negative pressure ventilation system.
Negative pressure ensures the air pressure inside the room is lower than the surrounding areas. This causes air to flow into the room when the door is opened, preventing contaminated air from escaping. Air removed from the AIIR is exhausted directly outside or passed through a High-Efficiency Particulate Air (HEPA) filter.
Anyone entering the AIIR must wear a National Institute for Occupational Safety and Health (NIOSH)-approved N95 respirator. This respirator filters out at least 95% of airborne particles, including droplet nuclei. Staff must be fit-tested to ensure the respirator forms a tight seal.
If the patient must leave the isolation room, they must wear a surgical mask to contain respiratory secretions. Patient transport must be limited to only necessary movements.
Determining Non-Infectiousness
Airborne Precautions remain in place until medical professionals determine the patient is no longer infectious. This decision relies on meeting specific clinical and laboratory criteria, starting with clinical improvement, meaning symptoms such as cough are resolving.
Duration of Treatment
A minimum of two weeks of appropriate, effective antibiotic therapy must be completed. Effective treatment quickly reduces the number of viable bacteria being expelled, minimizing transmission risk.
Laboratory Confirmation
The most objective criterion relies on laboratory testing of respiratory secretions. The patient must have three consecutive negative sputum smear results for acid-fast bacilli (AFB). These specimens are collected on different days, typically 8 to 24 hours apart.
Once all three criteria are satisfied—clinical improvement, sufficient time on treatment, and three consecutive negative sputum smears—the patient is considered non-infectious, and Airborne Precautions can be safely discontinued.