LEV is a source-control technique used for capturing airborne contaminants before they disseminate into the general environment. Guidelines recommend the use of LEV for cough-inducing and aerosol-generating procedures. If LEV is not feasible, cough-inducing and aerosol-generating procedures should be performed in a room that meets the requirements for an airborne infection isolation room (AIIR)⁷.

There are two basic types of local exhaust devices: complete enclosures (e.g., booths or tents) and partial enclosures (e.g., hoods). The former is the preferred type. Air from complete enclosures is HEPA-filtered and then can be exhausted outdoors or returned to the room. Complete enclosures should have sufficient airflow such that at least 99% of airborne particles can be removed during the interval between turnover of room air. Partial enclosures do not fully enclose the patient. Air is drawn across the patient's breathing zone and HEPA-filtered, then discharged back into the room or exhausted outdoors directly. The air velocity at the patient's breathing zone of partial enclosures should be kept above at least 200 feet per minute (FPM) to capture droplet nuclei^7,9.

Air-cleaning methods are considered an adjunct to other ventilation measures. They do not replace ventilation systems; rather, they should be considered as a complementary intervention. Such uses can increase the number of equivalent ACH in the room or area.

A negative pressure isolation room (NPIR) is a single-occupancy patient-care room used to isolate persons with a suspected or confirmed airborne infectious disease. Some guidelines distinguish AIIR from NPIR to describe the purpose for and details of ventilation of the rooms. NPIRs should provide negative pressure in the room so that air should flow from corridors (cleaner areas) into isolation rooms (less clean areas) to prevent the spread of contaminants; and direct exhaust of air from the room to the outside of the building or recirculation of air through a HEPA filter before returning to circulation. Korean regulations for government-designated isolation room recommend airflow of ≥12 ACH when feasible, along with current CDC and WHO recommendation¹⁴. The minimum negative pressure differential should be ≥2.5 Pa (0.01" water gauge), maintaining the size of value as follows; bathroom≥isolation room≥anteroom>corridors. Results of air flow patterns should be monitored and documented daily¹⁴. Table 2 summarizes the comparison of regulations and guidelines for NPIRs.

The two types of respirators are powered air-purifying respirators (PAPRs) and non-PAPRs. Non-PAPRs that are certified by CDC/National Institute for Occupational Safety and Health (NIOSH) comprise nine classes of respirators including N (not resistant to oil) series, R (resistant to oil) series, and P (oil proof) series that have 95%, 99%, and 100% (99.7%) filtration efficiency, respectively, when challenged with 0.3 µm particles. PAPRs use a blower that draws air into the facepiece through filters and which are classified as high efficiency, and meet N100, R100, and P100 criteria. A tight-fitting or loose-fitting facepiece, helmet, or hood can be equipped with PAPRs⁷. For protection against TB, guidelines recommend particulate respirators that meet or exceed the N95 standards set by CDC/NIOSH or the FFP2 standards that are European Conformity (CE) certified. Either non-PAPRs with N95, N99, N100, R95, R99, R100, P95, P99, and P100 filters, or PAPRs with high efficiency filters can be used^6,7.

Respirators are available in a wide range of colors, shapes, sizes, and styles. The configurations are not standardized across models. Some N95 respirators have an exhalation valve on the front, which reduces exhalation resistance and makes it easier to breathe. Some styles will fit individuals better than others and certain styles may be more comfortable and have better fitting characteristics²¹. There does not appear to be a single best fitting respirator. Instead, studies demonstrate that fit testing programs can be designed to successfully fit nearly all workers with existing products²². Fit testing provides a means to determine which respirator model and size fits the wearer best as well as to confirm that the wearer can don the respirator properly. As long as the respirators exceed the NIOSH-approved N95 standards, have been fit tested, and are being used appropriately, then wearer can use them regardless of the model²¹.

Some special circumstances should be considered for selection of respirators. For situations in which the risk for exposure to M. tuberculosis is especially high because of cough-inducing and aerosol-generating procedures (e.g., bronchoscopy), more protective respirators such as PAPRs should be considered^7,23,24. PAPRs can also be useful for persons with facial hair or other conditions that prevent an adequate face to facepiece seal. On the other hand, when surgical procedures (or other procedures requiring a sterile field) are performed, respirators with exhalation valves or PAPRs should not be used because they do not protect the sterile field⁷.

Two methods of fit testing are quantitative (QNFT) and qualitative fit testing (QLFT). Nowadays, the former serves as the gold standard. QNFT is an assessment of the adequacy of fit by numerically measuring the ratio of specific particles in the air inside and outside the breathing zone using an electronic device, which directly reflects the quantity of leakage. In contrast, the QLFT only measures the presence of leakage by an individual's response to a test agent such as isoamyl acetate or irritant smoke near the wearer's nose while wearing the respirator²⁵.

A given N95 respirator may fit only 0%-69% of wearers^26,27. Other studies suggested a fit test passing rate of at least 90% of randomly selected wearers^28,29. Training in respirator donning can improve passing a fit-test and result in an increase in protection^27,28,30.

The user must be fit tested in each respirator model before wearing a respirator. Fit testing should be performed during the initial respiratory-protection program training and periodically thereafter, based on the risk assessment of the setting and in accordance with applicable central or local government regulations⁷.

Aside from fit test, performing a fit check (user-seal check) on a respirator before each use is always necessary to minimize contaminant leakage into the facepiece. Because passing a fit test does not guarantee that an adequate fit will always be achieved, to go on achieving this, the wearer must perform the user fit check each time that he or she dons a respirator³¹.

The fit checks for respirators are described in each user instruction from manufacturer. There are two types of fit checks; positive-pressure and negative-pressure checks. In each method, the wearer should cover the surface of the respirator and gently exhale or inhale. If the wearer feels air leaking around the face seal when exhaling or if the respirator is not drawn in toward the face when inhaling, the fit check was not successful. The respirator should be examined for any defects and readjusted. If the check is not successful despite of repeated attempts, new respirator should be tried⁷.

Fit check is a simple, inexpensive, fast, and self-manageable test that can be conducted anytime and anywhere. However, this test is unable to serve as an effective alternative to QNFT because of its low sensitivity, accuracy, and predictive value^25,26,32,33. Training wearers how to fit check increases the possibility that they will adjust respirators to proper fit³⁴.