Negative Pressure Room

What is a negative pressure room

A negative pressure room, also known as a “negative pressure isolation room” is a controlled, critical area, which maintains a negative pressure differential to a non-controlled space. The need for such controlled spaces has increased dramatically in light of the COVID-19 pandemic. Most U.S. hospitals use negative-pressure airborne infection isolation rooms (AIIRs) to house patients with suspected or confirmed airborne transmissible infections such as COVID-19. When a patient is positively diagnosed, they are typically isolated in a room which maintains negative pressure at all times. This protects the general public, hospital/healthcare workers, and others from cross-contamination.

A negative pressure isolation room is monitored constantly for negative pressure. This measurement is usually on a “pascal” scale (Pa) or may also be measured in “inches of water column” (WC). In a negative pressure room, the air pressure is lower than adjacent spaces, or “negative.” This simply means that when the door of a isolation room is opened, air is sucked in to the room, instead of being pushed out. This forces all airborne pathogens, particulates and microbial contaminants to remain in the isolation room and not escape into generally populated areas.

On the opposite end of things, a positive pressure room pushes air out when a door or window is opened. These positive pressure areas are ideal for cleanrooms where the highest level of cleanliness is required for pharmaceutical manufacturing, surgical rooms, technology manufacturing, sterile manufacturing, etc. In the case of a positive pressure room, all air is pushed out, thereby preventing outside contaminants from entering.

There are four types of isolation rooms, two of which are negative pressure rooms.

  • Neutral or standard room air pressure, for example standard air conditioning, also known as Class S
  • Positive room air pressure where an immune-compromised patient is protected from airborne transmission of any infection, Class P
  • Negative room air pressure, where others are protected from any airborne transmission from a patient who may be an infection risk, Class N
  • Negative room air pressure with additional barriers including an Anteroom, also known as Class Q for quarantine isolation (COVID-19, Tuberculosis, etc.) .

How does a negative pressure room work

Negative pressure is generated and maintained by a ventilation system that removes more air from the room than is allowed to enter the room.  With a negative pressure room outside air flows into the room through a gap under the door (typically about one half-inch high). Except for this gap, the room is as airtight as possible.  All other cracks and gaps, such as those around windows, light fixtures and electrical outlets are sealed, since leakage through these gaps can compromise or eliminate room negative pressure.

Because generally there are components of the exhausted air such as chemical contaminants, microorganisms, or radioactive isotopes that must not be released to the surrounding outdoor environment (indeed, the original purpose of the negative-pressure room), any air outlet must, at a minimum, be located such that it will not expose people or other occupied spaces.  In a negative pressure room exhaust air is exhausted through the roof of the building. However, in some cases, such as when highly infections microorganisms are present, for example in a biosafety level 4 room, the air must first be mechanically filtered or disinfected by ultraviolet irradiation or chemical means before being released to the surrounding outdoor environment. In the case of nuclear facilities the air is monitored for the presence of radioactive isotopes and usually filtered before being exhausted through a tall exhaust duct to be released higher in the air away from occupied spaces.

To maintain a negative pressure in isolation rooms two areas must be considered;  the room itself and the corridor or hall directly outside the room.

  • For AIIR, the room should be negatively pressurized in relation to the corridor. This helps to prevent infectious particles from escaping the room envelope. If an anteroom is present between the AIIR and the corridor, the AIIR may be negatively or positively pressurized compared to the anteroom. However, if the AIIR is positively pressurized to the anteroom, the anteroom must be negatively pressurized to the corridor.
  • A difference in pressure always causes air to move from areas at higher pressure to those at lower pressure. The greater the pressure difference, the faster the air will move. This air movement helps provide containment of infectious particles by moving the air from a clean area to a less clean area.
  • The differential pressure or pressure offset between the two areas is established by mechanically adjusting the supply and exhaust air. For a negative pressure room, the sum of the mechanically exhausted air must exceed the sum of the mechanically supplied air. This offset forces air to enter the room under the door and through other leaks thus preventing infectious particles from escaping.
  • In order to maintain consistent offset airflow, the difference between exhaust and supply should create a pressure differential of at least 0.01 inch water gauge (wg) or 2.5 Pascals (Pa).  Pressure in this application is used to move the air from adjacent spaces into the isolation room.

Hospital negative pressure room

Creating positive and negative pressure rooms requires the use of specialized construction and climate control equipment. A minimum of 12 air-flow changes each hour (ACH) must be maintained.  In some situations even greater ACH may be required.  The following must also be addressed:

  • The recirculation of air through HEPA filters to control the movement of airborne contaminants;
  • Self-closing entryway with an adequate seal must be provided;
  • Thoroughly sealing floors, ceiling, walls, and windows;
  • Properly sized fans and ductwork must be specified to move air in the desired directions;
  • A monitoring system that allows users to adjust pressure when necessary;
  • Intermediate environment between the pressure room and outside environment for deliveries, observations, and protective gear storage must be provided.

Some medical facilities additionally incorporate UV radiation into the system to help maintain a sterile environment. Using UV light in a filtration system sterilizes particles and reduces viruses (such as coronavirus) in the quarantine space, helping to protect healthcare workers who enter the room to service the quarantined patient.

Once the area is in service, terminal cleaning should occur, after sufficient time has elapsed for enough air flow to remove potentially infectious particles. For information on determining air changes per hour (ACH), see this instructional video. The facility should determine the desired efficiency for removal based on the CDC table duplicated below. The original table and references in the note may be found at the following link:


2 138 207
4 69 104
6+ 46 69
8 35 52
10+ 28 41
12+ 23 35
15+ 18 28
20 14 21
50 6 8

Patient Placement

The CDC recommends the following for patients positively identified as infected with COVID-19 virus:

  • Evaluate the need for hospitalization. If hospitalization is not medically necessary, home care is preferable if the individual’s situation allows.
  • If admitted to a hospital, place a patient with suspected or confirmed SARS-CoV-2 infection in a single-person room with the door closed. The patient should have a dedicated bathroom.
    • Airborne Infection Isolation Rooms (AIIRs) should be reserved for patients who will be undergoing aerosol generating procedures
  • Personnel entering the room should use PPE as described below.
  • As a measure to limit Health Care Partners (HCP) exposure and conserve personal protective equipment (PPE), facilities could consider designating entire units within the facility, with dedicated HCP, to care for patients with suspected or confirmed SARS-CoV-2 infection. Dedicated means that HCP are assigned to care only for these patients during their shift.
    • Determine how staffing needs will be met as the number of patients with suspected or confirmed SARS-CoV-2 infection increase and if HCP become ill and are excluded from work.
    • It might not be possible to distinguish patients who have COVID-19 from patients with other respiratory viruses. As such, patients with different respiratory pathogens might be cohorted on the same unit. However, only patients with the same respiratory pathogen may be housed in the same room. For example, a patient with COVID-19 should ideally not be housed in the same room as a patient with an undiagnosed respiratory infection or a respiratory infection caused by a different pathogen.
  • To the extent possible, patients with suspected or confirmed SARS-CoV-2 infection should be housed in the same room for the duration of their stay in the facility (e.g., minimize room transfers).
  • Limit transport and movement of the patient outside of the room to medically essential purposes.
    • Whenever possible, perform procedures/tests in the patient’s room.
    • Consider providing portable x-ray equipment in patient cohort areas to reduce the need for patient transport.
  • Communicate information about patients with suspected or confirmed SARS-CoV-2 infection to appropriate personnel before transferring them to other departments in the facility (e.g., radiology) and to other healthcare facilities.
  • Patients should wear a facemask or cloth face covering to contain secretions during transport. If patients cannot tolerate a facemask or cloth face covering or one is not available, they should use tissues to cover their mouth and nose while out of their room.
  • Once the patient has been discharged or transferred, HCP, including environmental services personnel, should refrain from entering the vacated room until sufficient time has elapsed for air changing equipment to remove potentially infectious particles (more information on clearance rates under differing ventilation conditions is available). Once this time has elapsed, the room should undergo appropriate cleaning and surface disinfection before it is returned to routine use.

In addition to these minimal recommendations, the CDC also advises the use of a dependable and accurate. monitoring system for maintaining secure AIIR standards.

CDC negative pressure room requirements

Airborne infection isolation (AII) refers to the isolation of patients infected with organisms spread via airborne droplet nuclei <5 µm in diameter. This isolation area receives numerous air changes per hour (ACH) (>12 ACH for new construction as of 2001; >6 ACH for construction before 2001), and is under negative pressure, such that the direction of the air flow is from the outside adjacent space (e.g., the corridor) into the room. The air in an AII room is preferably exhausted to the outside of a building, but may be recirculated provided that the return air is filtered through a high-efficiency particulate air (HEPA) filter. The use of personal respiratory protection is also indicated for persons entering these rooms when caring for TB or smallpox patients and for staff who lack immunity to airborne viral diseases (e.g., measles or varicella zoster virus [VZV] infection).

Protective environment (PE) is a specialized patient-care area, usually in a hospital, with a positive air flow relative to the corridor (i.e., air flows from the room to the outside adjacent space). The combination of HEPA filtration, high numbers of air changes per hour (>12 ACH), and minimal leakage of air into the room creates an environment that can safely accommodate patients who have undergone allogeneic hematopoietic stem cell transplant (HSCT).


I. Air-Handling Systems in Health-Care Facilities

Use AIA guidelines as minimum standards where state or local regulations are not in place for design and construction of ventilation systems in new or renovated health-care facilities. Ensure that existing structures continue to meet the specifications in effect at the time of construction (1). Category IC (AIA: 1.1.A, 5.4)
Monitor ventilation systems in accordance with engineers’ and manufacturers’ recommendations to ensure preventive engineering, optimal performance for removal of particulates, and elimination of excess moisture (1–8). Category IB, IC (AIA: 7.2, 7.31.D, 8.31.D, 9.31.D, 10.31.D, 11.31.D, Environmental Protection Agency [EPA] guidance)

1. Ensure that heating, ventilation, air conditioning (HVAC) filters are properly installed and maintained to prevent air leakages and dust overloads (2,4,6,9). Category IB
2. Monitor areas with special ventilation requirements (e.g., AII or PE) for ACH, filtration, and pressure differentials (1,7,8,10–26). Category IB, IC (AIA: 7.2.C7, 7.2.D6)

a. Develop and implement a maintenance schedule for ACH, pressure differentials, and filtration efficiencies by using facility-specific data as part of the multidisciplinary risk assessment. Take into account the age and reliability of the system.
b. Document these parameters, especially the pressure differentials.

3. Engineer humidity controls into the HVAC system and monitor the controls to ensure adequate moisture removal (1). Category IC (AIA: 7.31.D9)

a. Locate duct humidifiers upstream from the final filters.
b. Incorporate a water-removal mechanism into the system.
c. Locate all duct takeoffs sufficiently downstream from the humidifier so that moisture is completely absorbed.

4. Incorporate steam humidifiers, if possible, to reduce potential for microbial proliferation within the system, and avoid use of cool-mist humidifiers. Category II
5. Ensure that air intakes and exhaust outlets are located properly in construction of new facilities and renovation of existing facilities (1,27). Category IC (AIA: 7.31.D3, 8.31.D3, 9.31.D3, 10.31.D3, 11.31.D3)

a. Locate exhaust outlets &gt;25 ft from air-intake systems.
b. Locate outdoor air intakes &gt;6 ft above ground or &gt;3 ft above roof level.
c. Locate exhaust outlets from contaminated areas above roof level to minimize recirculation of exhausted air.

6. Maintain air intakes and inspect filters periodically to ensure proper operation (1,11–16,27). Category IC (AIA: 7.31.D8)
7. Bag dust-filled filters immediately upon removal to prevent dispersion of dust and fungal spores during transport within the facility (4,28). Category IB

a. Seal or close the bag containing the discarded filter.
b. Discard spent filters as regular solid waste, regardless of the area from which they were removed (28).

8. Remove bird roosts and nests near air intakes to prevent mites and fungal spores from entering the ventilation system (27,29,30). Category IB
9. Prevent dust accumulation by cleaning air-duct grilles in accordance with facility-specific procedures and schedules and when rooms are not occupied by patients (1,10–16). Category IC, II (AIA: 7.31.D10)
10. Periodically measure output to monitor system function; clean ventilation ducts as part of routine HVAC maintenance to ensure optimum performance (1,31,32). Category IC, II (AIA: 7.31.D10)

Use portable, industrial-grade HEPA filter units capable of filtration rates in the range of 300–800 ft3/min to augment removal of respirable particles as needed (33). Category II

1. Select portable HEPA filters that can recirculate all or nearly all of the room air and provide the equivalent of &gt;12 ACH (34). Category II
2. Portable HEPA filter units placed in construction zones can be used later in patient-care areas, provided all internal and external surfaces are cleaned, and the filter replaced or its
performance verified by appropriate particle testing. Category II
3. Situate portable HEPA units with the advice of facility engineers to ensure that all room air is filtered (34). Category II
4. Ensure that fresh-air requirements for the area are met (33,35). Category II

Follow appropriate procedures for use of areas with through-the-wall ventilation units (1). Category IC (AIA: 8.31.D1, 8.31.D8, 9.31.D23, 10.31.D18, 11.31.D15)

1. Do not use such areas as PE rooms (1). Category IC (AIA: 7.2.D3)
2. Do not use a room with a through-the-wall ventilation unit as an AII room unless it can be demonstrated that all required AII engineering controls are met (1,34). Category IC (AIA:7.2.C3)

Conduct an infection-control risk assessment (ICRA) and provide an adequate number of AII and PE rooms (if required) or other areas to meet the needs of the patient population (1,2,7,8,17,19, 20,34,36–43). Category IA, IC (AIA: 7.2.C, 7.2.D)
When ultraviolet germicidal irradiation (UVGI) is used as a supplemental engineering control, install fixtures 1) on the wall near the ceiling or suspended from the ceiling as an upper air unit; 2) in the air-return duct of an AII area; or 3) in designated enclosed areas or booths for sputum induction (34). Category II
Seal windows in buildings with centralized HVAC systems, including PE areas (1,3,44). Category IB, IC (AIA: 7.2.D3)
Keep emergency doors and exits from PE rooms closed except during an emergency; equip emergency doors and exits with alarms. Category II
Develop a contingency plan for backup capacity in the event of a general power failure (45). Category IC (Joint Commission on Accreditation of Healthcare Organizations [JCAHO]: Environment of Care [EC] 1.4)

1. Emphasize restoration of appropriate air quality and ventilation conditions in AII rooms, PE rooms, operating rooms, emergency departments, and intensive care units (1,45). Category IC (AIA: 1.5.A1; JCAHO: EC 1.4)
2. Deploy infection-control procedures to protect occupants until power and systems functions are restored (1,36,45). Category IC (AIA: 5.1, 5.2; JCAHO: EC 1.4)

Do not shut down HVAC systems in patient-care areas except for maintenance, repair, testing of emergency backup capacity, or new construction (1,46). Category IB, IC (AIA: 5.1, 5.2.B, C)

1. Coordinate HVAC system maintenance with infection-control staff and relocate immunocompromised patients if necessary (1). Category IC (AIA: 5.1, 5.2)
2. Provide backup emergency power and air-handling and pressurization systems to maintain filtration, constant ACH, and pressure differentials in PE rooms, AII rooms, operating rooms, and other critical-care areas (1,37,47). Category IC (AIA: 5.1, 5.2)
3. For areas not served by installed emergency ventilation and backup systems, use portable units and monitor ventilation parameters and patients in those areas (33). Category II
4. Coordinate system startups with infection-control staff to protect patients in PE rooms from bursts of fungal spores (1,3,37,47). Category IC (AIA: 5.1, 5.2)
5. Allow sufficient time for ACH to clean the air once the system is operational (Table 1) (1,33). Category IC (AIA: 5.1, 5.2)

HVAC systems serving offices and administrative areas may be shut down for energy conservation purposes, but the shutdown must not alter or adversely affect pressure differentials maintained in laboratories or critical-care areas with specific ventilation requirements (i.e., PE rooms, AII rooms, operating rooms).

Category II
Whenever possible, avoid inactivating or shutting down the entire HVAC system, especially in acute-care facilities.

Category II
Whenever feasible, design and install fixed backup ventilation systems for new or renovated construction of PE rooms, AII rooms, operating rooms, and other critical-care areas identified by ICRA (1). Category IC (AIA: 1.5.A1)
II. Construction, Renovation, Remediation, Repair, and Demolition

Establish a multidisciplinary team that includes infection-control staff to coordinate demolition, construction, and renovation projects and consider proactive preventive measures at the inception; produce and maintain summary statements of the team’s activities (1,9,11–16,38,48–51). Category IB, IC (AIA: 5.1)
Educate both the construction team and health-care staff in immunocompromised patient-care areas regarding the airborne infection risks associated with construction projects, dispersal of fungal spores during such activities, and methods to control the dissemination of fungal spores (11–16,27,50,52–56).

Category IB
Incorporate mandatory adherence agreements for infection control into construction contracts, with penalties for noncompliance and mechanisms to ensure timely correction of problems (1,11,13–16,27,50). Category IC (AIA: 5.1)
Establish and maintain surveillance for airborne environmental disease (e.g., aspergillosis) as appropriate during construction, renovation, repair, and demolition activities to ensure the health and safety of immunocompromised patients (27,57–59). Category IB

1. Using active surveillance, monitor for airborne infections in immunocompromised patients (27,37,57,58). Category IB
2. Periodically review the facility’s microbiologic, histopathologic, and postmortem data to identify additional cases (27,37,57,58). Category IB
3. If cases of aspergillosis or other health-care–associated airborne fungal infections occur, aggressively pursue the diagnosis with tissue biopsies and cultures as feasible (11,13–16,27,50,57–59). Category IB

Implement infection-control measures relevant to construction, renovation, maintenance, demolition, and repair (1,16,49,50,60). Category IB, IC (AIA: 5.1, 5.2)

1. Before the project gets under way, perform an ICRA to define the scope of the activity and the need for barrier measures (1,11,13–16,48–51,60). Category IB, IC (AIA: 5.1)

a. Determine if immunocompromised patients may be at risk for exposure to fungal spores from dust generated during the project (13–16,48,51).
b. Develop a contingency plan to prevent such exposures (13–16,48,51).

2. Implement infection-control measures for external demolition and construction activities (11,13–16,50,61,62). Category IB

a. Determine if the facility can operate temporarily on recirculated air; if feasible, seal off adjacent air intakes.
b. If this is not possible or practical, check the low-efficiency (roughing) filter banks frequently and replace as needed to avoid buildup of particulates.
c. Seal windows and reduce wherever possible other sources of outside air intrusion (e.g., open doors in stairwells and corridors), especially in PE areas.

3. Avoid damaging the underground water system (i.e., buried pipes) to prevent soil and dust contamination of the water (1,63). Category IB, IC (AIA: 5.1)
4. Implement infection-control measures for internal construction activities (1,11,13–16,48– 50,64). Category IB, IC (AIA: 5.1, 5.2)

a. Construct barriers to prevent dust from construction areas from entering patient-care areas; ensure that barriers are impermeable to fungal spores and in compliance with local fire codes (1,45,48,49,55,64–66).
b. Seal off and block return air vents if rigid barriers are used for containment (1,16,50).
c. Implement dust-control measures on surfaces and divert pedestrian traffic away from work zones (1,48,49,64).
d. Relocate patients whose rooms are adjacent to work zones, depending on their immune status, the scope of the project, the potential for generation of dust or water aerosols, and the methods used to control these aerosols (1,64,65).

5. Perform those engineering and work-site related infection-control measures as needed for internal construction, repairs, and renovations (1,48,49,51,64,66). Category IB, IC (AIA:5.1, 5.2)

a. Ensure proper operation of the air-handling system in the affected area after erection of barriers and before the room or area is set to negative pressure (39,47,50,64). Category IB

b. Create and maintain negative air pressure in work zones adjacent to patient-care areas and ensure that required engineering controls are maintained (1,48,49,51,64,66).
c. Monitor negative airflow inside rigid barriers (1,67).
d. Monitor barriers and ensure integrity of the construction barriers; repair gaps or breaks in barrier joints (1,65,66,68).
e. Seal windows in work zones if practical; use window chutes for disposal of large pieces of debris as needed, but ensure that the negative pressure differential for the area is maintained (1,13,48).
f. Direct pedestrian traffic from construction zones away from patient-care areas to minimize dispersion of dust (1,13–16,44,48–51,64).
g. Provide construction crews with 1) designated entrances, corridors, and elevators wherever practical; 2) essential services (e.g., toilet facilities) and convenience services (e.g., vending machines); 3) protective clothing (e.g., coveralls, footgear, and headgear) for travel to patient-care areas; and 4) a space or anteroom for changing clothing and storing equipment (1,11,13–16,50).
h. Clean work zones and their entrances daily by 1) wet-wiping tools and tool carts before their removal from the work zone; 2) placing mats with tacky surfaces inside the entrance; and 3) covering debris and securing this covering before removing debris from the work zone (1,11,13–16,50).
i. In patient-care areas, for major repairs that include removal of ceiling tiles and disruption of the space above the false ceiling, use plastic sheets or prefabricated plastic units to contain dust; use a negative pressure system within this enclosure to remove dust; and either pass air through an industrial-grade, portable HEPA filter capable of filtration rates of 300–800 ft3/min., or exhaust air directly to the outside (16,50,64,67,69).
j. Upon completion of the project, clean the work zone according to facility procedures, and install barrier curtains to contain dust and debris before removing rigid barriers (1,11,13–16,48–50).
k. Flush the water system to clear sediment from pipes to minimize waterborne microorganism proliferation (1,63).
l. Restore appropriate ACH, humidity, and pressure differential; clean or replace air filters; dispose of spent filters (3,4,28,47).

Use airborne-particle sampling as a tool to evaluate barrier integrity (3,70). Category II
Commission the HVAC system for newly constructed health-care facilities and renovated spaces before occupancy and use, with emphasis on ensuring proper ventilation for operating rooms, AII rooms, and PE areas (1,70–72). Category IC (AIA: 5.1; ASHRAE: 1-1996)
No recommendation is offered regarding routine microbiologic air sampling before, during, or after construction, or before or during occupancy of areas housing immunocompromised patients (9,48,49,51,64,73,74).

Unresolved issue
If a case of health-care–acquired aspergillosis or other opportunistic environmental airborne fungal disease occurs during or immediately after construction, implement appropriate follow-up measures (40,48,75–78). Category IB

1. Review pressure-differential monitoring documentation to verify that pressure differentials in the construction zone and in PE rooms are appropriate for their settings (1,40,78). Category IB, IC (AIA: 5.1)
2. Implement corrective engineering measures to restore proper pressure differentials as needed (1,40,78). Category IB, IC (AIA: 5.1)
3. Conduct a prospective search for additional cases and intensify retrospective epidemiologic review of the hospital’s medical and laboratory records (27,48,76,79,80). Category IB
4. If no epidemiologic evidence of ongoing transmission exists, continue routine maintenance in the area to prevent health-care–acquired fungal disease (27,75). Category IB

If no epidemiologic evidence exists of ongoing transmission of fungal disease, conduct an environmental assessment to find and eliminate the source (11,13–16,27,44,49–51,60,81). Category IB

1. Collect environmental samples from potential sources of airborne fungal spores, preferably by using a high-volume air sampler rather than settle plates (2,4,11,13–16,27,44,49,50,64,65,81–86). Category IB
2. If either an environmental source of airborne fungi or an engineering problem with filtration or pressure differentials is identified, promptly perform corrective measures to eliminate the source and route of entry (49,60). Category IB
3. Use an EPA-registered antifungal biocide (e.g., copper-8-quinolinolate) for decontaminating structural materials (16,61,66,87). Category IB
4. If an environmental source of airborne fungi is not identified, review infection-control measures, including engineering controls, to identify potential areas for correction or improvement (88,89). Category IB
5. If possible, perform molecular subtyping of Aspergillus spp. isolated from patients and the environment to compare their strain identities (90–94). Category II

If air-supply systems to high-risk areas (e.g., PE rooms) are not optimal, use portable, industrial-grade HEPA filters on a temporary basis until rooms with optimal air-handling systems become available (1,13–16,27,50). Category II

III. Infection Control and Ventilation Requirements for PE rooms

Minimize exposures of severely immunocompromised patients (e.g., solid-organ transplant patients or allogeneic neutropenic patients) to activities that might cause aerosolization of fungal spores (e.g., vacuuming or disruption of ceiling tiles) (37,48,51,73). Category IB
Minimize the length of time that immunocompromised patients in PE are outside their rooms for diagnostic procedures and other activities (37,62). Category IB
Provide respiratory protection for severely immunocompromised patients when they must leave PE for diagnostic procedures and other activities; consult the most recent revision of CDC’s Guideline for Prevention of Health-Care–Associated Pneumonia for information regarding the appropriate type of respiratory protection. (27,37). Category II
Incorporate ventilation engineering specifications and dust-controlling processes into the planning and construction of new PE units (Figure 1). Category IB, IC

1. Install central or point-of-use HEPA filters for supply (incoming) air (1,2,27,48,56,70, 80,82,85,95–102). Category IB, IC (AIA: 5.1, 5.2, 7.2.D)
2. Ensure that rooms are well-sealed by 1) properly constructing windows, doors, and intake and exhaust ports; 2) maintaining ceilings that are smooth and free of fissures, open joints, and crevices; 3) sealing walls above and below the ceiling; and 4) monitoring for leakage and making any necessary repairs (1,27,44,100,101). Category IB, IC (AIA: 7.2.D3)
3. Ventilate the room to maintain &gt;12 ACH (1,27,37,100,101,103). Category IC (AIA: 7.2.D)
4. Locate air supply and exhaust grilles so that clean, filtered air enters from one side of the room, flows across the patient’s bed, and exits from the opposite side of the room (1,27,100,101). Category IC (AIA: 7.31.D1)
5. Maintain positive room air pressure (&gt;2.5 Pa [0.01-inch water gauge]) in relation to the corridor (1,3,27,100,101). Category IB, IC (AIA: Table 7.2)
6. Maintain airflow patterns and monitor these on a daily basis by using permanently installed visual means of detecting airflow in new or renovated construction, or by using other visual methods (e.g., flutter strips or smoke tubes) in existing PE units. Document the monitoring results (1,13). Category IC (AIA: 7.2.D6)
7. Install self-closing devices on all room exit doors in PE rooms (1). Category IC (AIA: 7.2.D4)

Do not use laminar air flow systems in newly constructed PE rooms (99,101). Category II
Take measures to protect immunocompromised patients who would benefit from a PE room and who also have an airborne infectious disease (e.g., acute VZV infection or tuberculosis).

1. Ensure that the patient’s room is designed to maintain positive pressure.
2. Use an anteroom to ensure appropriate air-balance relationships and provide independent exhaust of contaminated air to the outside, or place a HEPA filter in the exhaust duct if the return air must be recirculated (1,100) (Figure 2). Category IC (AIA: 7.2.D1, A7.2.D)
3. If an anteroom is not available, place the patient in AII and use portable, industrial-grade HEPA filters to enhance filtration of spores in the room (33). Category II

Maintain backup ventilation equipment (e.g., portable units for fans or filters) for emergency provision of required ventilation for PE areas and take immediate steps to restore the fixed ventilation system (1,37,47). Category IC (AIA: 5.1)

IV. Infection-Control and Ventilation Requirements for AII Rooms

Incorporate certain specifications into the planning and construction or renovation of AII units (1,34,100,101,104) (Figure 3). Category IB, IC

1. Maintain continuous negative air pressure (2.5 Pa [0.01 inch water gauge]) in relation to the air pressure in the corridor; monitor air pressure periodically, preferably daily, with audible manometers or smoke tubes at the door (for existing AII rooms), or with a permanently installed visual monitoring mechanism. Document the results of monitoring (1,100,101). Category IC (AIA: 7.2.C7, Table 7.2)
2. Ensure that rooms are well-sealed by properly constructing windows, doors, and air-intake and exhaust ports; when monitoring indicates air leakage, locate the leak and make necessary repairs (1,99,100). Category IB, IC (AIA: 7.2.C3)
3. Install self-closing devices on all AII room exit doors (1). Category IC (AIA: 7.2.C4)
4. Provide ventilation to ensure &gt;12 ACH for renovated rooms and new rooms, and &gt;6 ACH for existing AII rooms (1,34,104). Category IB, IC (AIA: Table 7.2)
5. Direct exhaust air to the outside, away from air-intake and populated areas. If this is not practical, air from the room can be recirculated after passing through a HEPA filter (1,34). Category IC (AIA: Table 7.2)

Where supplemental engineering controls for air cleaning are indicated from a risk assessment of the AII area, install UVGI units in the exhaust air ducts of the HVAC system to supplement HEPA filtration or install UVGI fixtures on or near the ceiling to irradiate upper room air (34). Category II
Implement environmental infection-control measures for persons with diagnosed or suspected airborne infectious diseases.

1. Use AII rooms for patients with or suspected of having an airborne infection who also require cough-inducing procedures, or use an enclosed booth that is engineered to provide 1) &gt;12 ACH; 2) air supply and exhaust rate sufficient to maintain a 2.5 Pa (0.01-inch water gauge) negative pressure difference with respect to all surrounding spaces with an exhaust
rate of &gt;50 ft3/min; and 3) air exhausted directly outside away from air intakes and traffic or exhausted after HEPA filtration before recirculation (1,34,105–107). Category IB, IC (AIA: 7.15.E, 7.31.D23, 9.10, Table 7.2)
2. Although airborne spread of viral hemorrhagic fever (VHF) has not been documented in a health-care setting, prudence dictates placing a VHF patient in an AII room, preferably with an anteroom, to reduce the risk of occupational exposure to aerosolized infectious material in blood, vomitus, liquid stool, and respiratory secretions present in large amounts during the end stage of a patient’s illness (108–110). Category II

a. If an anteroom is not available, use portable, industrial-grade HEPA filters in the patient’s room to provide additional ACH equivalents for removing airborne particulates.
b. Ensure that health-care workers wear face shields or goggles with appropriate respirators when entering the rooms of VHF patients with prominent cough, vomiting, diarrhea, or hemorrhage (109).

3. Place smallpox patients in negative pressure rooms at the onset of their illness, preferably using a room with an anteroom, if available (36). Category II

No recommendation is offered regarding negative pressure or isolation for patients with Pneumocystis carinii pneumonia (111–113). Unresolved issue.
Maintain backup ventilation equipment (e.g., portable units for fans or filters) for emergency provision of ventilation requirements for AII rooms, and take immediate steps to restore the fixed ventilation system (1,34,47). Category IC (AIA: 5.1)

V. Infection-Control and Ventilation Requirements for Operating Rooms

Implement environmental infection-control and ventilation measures for operating rooms.

1. Maintain positive-pressure ventilation with respect to corridors and adjacent areas (1,114,115). Category IB, IC (AIA: Table 7.2)
2. Maintain &gt;15 ACH, of which &gt;3 ACH should be fresh air (1,116,117). Category IC (AIA: Table 7.2)
3. Filter all recirculated and fresh air through the appropriate filters, providing 90% efficiency (dust-spot testing) at a minimum (1,118). Category IC (AIA: Table 7.3)
4. In rooms not engineered for horizontal laminar airflow, introduce air at the ceiling and exhaust air near the floor (1,115,119). Category IC (AIA: 7.31.D4)
5. Do not use ultraviolet (UV) lights to prevent surgical-site infections (115,120–126). Category IB
6. Keep operating room doors closed except for the passage of equipment, personnel, and patients, and limit entry to essential personnel (127,128). Category IB

Follow precautionary procedures for infectious TB patients who also require emergency surgery (34,129,130). Category IB, IC

1. Use an N95 respirator approved by the National Institute for Occupational Safety and Health without exhalation valves in the operating room (129,131). Category IC (Occupational Safety and Health Administration [OSHA]; 29 Code of Federal Regulations [CFR] 1910.134,139)
2. Intubate the patient in either the AII room or the operating room; if intubating the patient in the operating room, do not allow the doors to open until 99% of the airborne contaminants are removed (Table 1) (34,117). Category IB
3. When anesthetizing a patient with confirmed or suspected TB, place a bacterial filter between the anesthesia circuit and patient’s airway to prevent contamination of anesthesia equipment or discharge of tubercle bacilli into the ambient air (130,132). Category IB
4. Extubate and allow the patient to recover in an AII room (34,117). Category IB
5. If the patient has to be extubated in the operating room, allow adequate time for ACH to clean 99% of airborne particles from the air (Table 1), because extubation is a cough-producing procedure (34,117). Category IB

Use portable, industrial-grade HEPA filters temporarily for supplemental air cleaning during intubation and extubation for TB patients who require surgery (33,34,117). Category II

1. Position the units appropriately so that all room air passes through the filter; obtain engineering consultation to determine the appropriate placements (34). Category II
2. Switch the portable unit off during the surgical procedure. Category II
3. Provide fresh air as per ventilation standards for operating rooms; portable units do not meet the requirements for the number of fresh ACH (1,33,133). Category II

If possible, schedule TB patients as the last surgical cases of the day to maximize the time available for removal of airborne contamination. Category II
No recommendation is offered for performing orthopedic implant operations in rooms supplied with laminar airflow (118,120). Unresolved issue
Maintain backup ventilation equipment (e.g., portable units for fans or filters) for emergency ventilation of operating rooms, and take immediate steps to restore the fixed ventilation system (1,47,131,134). Category IB, IC (AIA: 5.1)

VI. Other Potential Infectious Aerosol Hazards in Health-Care Facilities

In settings where surgical lasers are used, wear appropriate personal protective equipment (PPE), including N95 or N100 respirators, to minimize exposure to laser plumes (129,135,136). Category IC (OSHA; 29 CFR 1910.134,139)
Use central wall suction units with in-line filters to evacuate minimal laser plumes (135–138). Category II
Use a mechanical smoke evacuation system with a high-efficiency filter to manage the generation of large amounts of laser plume, when ablating tissue infected with human papilloma virus (HPV) or performing procedures on a patient with extrapulmonary TB (34,136,137,139–141). Category II


Negative room pressure monitor

Installing a Permanent Room Pressure Monitor

After a new AIIR is constructed and before it is occupied, the mechanical contractor will adjust the airflow quantities as directed by the engineer to ensure that it operates as designed. However, mechanical systems do drift out of balance over time. It is important to regularly check that an AIIR is still operating under negative pressure; planning for this should be included in the initial mechanical design of the room.

Room pressure monitors should be used as a supplement to daily visual checks when the room is in use. The most reliable way to monitor negative pressure is to install a permanent electronic room pressure monitor as part of the construction project. When properly selected and installed, a room pressure monitor can provide continuous qualitative and quantitative confirmation of negative pressure across a room boundary.

There are two common types of permanent pressure monitors: those that measure and display the actual air pressure difference between the AIIR and the reference space; and those that measure and display the actual air pressure difference between the AIIR and the reference space as well as chart, log and record all monitored variables.

Either type is suitable for an AIIR, but monitors which record and log values provide a pressure history so that if an unacceptable pressure reading occurred when no person was present the deviation will be known. Pressure differentials across room boundaries can be very small, often in the range of thousandths of an inch. For example, the CDC Guidelines recommend that negative pressure be at least ≥ 0.01″ of water gauge. Some devices that measure differential pressure are not accurate to this level. Before specifying or purchasing a room pressure monitor, make sure that the device is capable of accurately and reliably measuring a pressure difference this small.

Alarm(s) and Controls

In addition to providing a continuous readout of the pressure difference, the wall panel should include an audible and visual alarm to warn staff when pressurization is lost. The alarm will sound when the measured room pressurization drifts to less than the monitor’s reference pressure value. Reference pressure valves are programmed into the unit by an engineer or trained staff member. It will be a value between the steady state pressure differential maintained by the room and zero (neutral pressure). For example, in a room with a steady state pressure differential of minus 0.03″ W.G., the alarm could be programmed to activate when the pressure differential rises to minus 0.001″ W.G.. Minus 0.001″ W.G. is the reference pressure value. The wall panel should also allow staff to program a built-in time delay between loss of pressurization and alarm activation. The time delay will allow staff a sufficient interval to routinely enter and leave the room without setting off the alarm.

A typical time delay is 30 to 45 seconds. The audible alarm is usually a beeping sound, which will stop when negative pressure is restored or when a “mute” button on the panel is pressed. The visual alarm usually consists of a red warning light and/or a flashing message on the LCD. Most wall panels also have a green “normal” or “safe” light, which indicates that the monitor is operating and negative pressure is within programmed parameters.

Remote Alarm

In addition to the alarm included on the wall panel, most room pressure monitors include an extra identical signal that allows a “safe” or “alarm” signal to be sent from the wall panel to a remote location. Common locations for this remote alarm are the nurses’ station, the engineering department, and the central switchboard. It is usually possible to connect the alarm signals from a number of AIIR monitors to a remote alarm panel. In California, for example, the hospital building codes require that AIIRs be equipped with an alarm that annunciates at the room and at a nurses’ station or other suitable location. Ideally, the room pressure monitor would integrate with the facility building management system; i.e. BACnet.

Other Optional Features

There are a number of room pressure monitors available with additional options. Examples of such options include: the ability to receive text alerts, email alerts and automated phone calls if room pressure readings/values fall outside desired operating ranges. Other options might be the ability to generate log reports, and plot values over a specified period of time.


Negative pressure isolation rooms, AIIR rooms, and critically controlled environments are becoming more and more common – and more important. Maintaining room pressure (negative or positive) is critical for controlled applications where human health and wellness are considered. Just as important as controlling critical environments is monitoring these spaces to ensure they maintain proper pressure differentials, air changes, and warning systems.