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Is it permissible under current CDC and WHO airborne infection isolation room (AIIR) guidelines for two adjacent AIIRs to share a common anteroom?

In the situation in question, the shared anteroom has two doors. Each anteroom door facilitates transiting to the associated AIIR door. The shared anteroom is equipped with a single exhaust duct. There is no dividing wall in the middle of the anteroom.

A common situation at the hospital in question is that only one of the two AIIRs might be occupied at any given time by a patient on airborne infection precautions (AIP) for ruleout or confirmed TB. This appears to create a couple of potential problems.

First, if the staff leave the anteroom door open to the AIIR that is not being used for AIP, then the pressure differential between the anteroom and the hallway could be lessened (and perhaps even eliminated), thus reducing the function of the anteroom in buffering pressure changes between the hallway and AIIR that is in active use. This in turn could reduce or eliminate the ability of the shared anteroom to capture any fugitive droplet nuclei that could potentially escape from AIIR being used for AIP when staff enter/exit.

The other potential issue is if a shared anteroom could create a patient cohorting issue if the patients in each AIIR are infected with different respiratory pathogens, or if one patient has drug-susceptible TB and the other has MDR-TB?

Thank you in advance for your responses.

Paul A. Jensen, PhD, PE, CIH
Replied at 5:12 PM, 25 Jul 2013

Dear Daniel:

There is no prohibition to a shared anteroom for two separate patient AII rooms in the CDC "Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005."

The first issue is relatively simple . . . With infection prevention and control, it is necessary to rely on administrative controls first. Keeping doors closed is one of those controls and simple “visual” pressure differential devices and automatic door closers would help with this issue. If there is a failure of administrative controls, then keeping the door open between one of the two AII rooms and the anteroom may lead to deviation of the pressure differentials from the design. Is the design for decreasing pressure from the hallway to anteroom to the AII room? Is the anteroom designed to be positive pressure relative to the AII rooms and the hallway? What are the various airflow rates. Do you want to share a set of mechanical drawings (PDF format) with the community?

As far as “cohorting” goes, this could be a challenge. Though not ideal, having patients with different strains of TB in AII rooms with an adjoining anteroom is not banned by the CDC GLs. To put this in context, most AII rooms do not even have anterooms.

I hope this information helps. Please feel free to ask for further clarity or need further information.

FYI, neither the WHO 1999 "Guidelines for the prevention of tuberculosis
in health care facilities in resource-limited settings" nor the 2009 "WHO policy on TB infection control in health-care facilities, congregate settings and households" address this issue.


Paul J

Edward Nardell, MD
Replied at 6:42 PM, 25 Jul 2013

Let me take a stab at this and also ask Paul Jensen to comment. There are
many things to be said.

CDC does not generally encourage anterooms because of the difficulty in
maintaining stepwise differential pressures so that they work properly.
They can be convenient places for hand washing and to put respirators,
gowns/gloves (in the case of contact isolation), but are not essential for
airborne isolation, save perhaps for Ebola or other highly contagious,
deadly organisms, even if predominantly contact spread. One might make the
case for XDR TB if isolation rooms with anterooms are available. As you
know, TB and MDR TB, if on EFFECTIVE treatment, become rapidly
non-infectious, making concerns about stray droplet nuclei more theoretical
than real. Since treatment for XDR may not be effective, proper isolation
is more critical.

Two negative pressure isolation rooms off one anteroom presents the
theoretical problems you state and probably others. Any organisms escaping
into the anteroom, if not cleared, could in theory be sucked into the other
negative pressure room. But this is also true of a string of adjacent
negative pressure rooms off an indoor corridor without an anteroom. I would
not want to be a HIV patient with suspected TB adjacent to a patient with
XDR with a common anteroom. Two MDR or two drug susceptible patients on
therapy are much less a concern.

Presumably this is not a resource-limited setting. If not, another
(probably unnecessary) approach would be to install upper room UVGI in the
anteroom, helping to further reduce potential room to room transfer of
organisms regardless of pressure. On the other hand, if negative pressure
isolation rooms without anterooms are allowed (encouraged), the anteroom is
usually not considered critical, and patients are being treated, perhaps
nothing other than regular pressure monitoring and maintenance need be

S. Mehtar
Replied at 7:43 AM, 30 Jul 2013

Dear Daniel
I just want to add my tuppence worth! If there is leaking to the anteroom, the negative pressure ventilation needs to be rechecked. There should be no leakage for a start. The anterooms in the UK and other countries is actually a gowning area as you well know so there should not be any problem if the two isolation rooms have independent ventilation.
It is worth remembering that in many parts of the world there are NO anterooms

Prof Shaheen Mehtar
MBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Eng)
Chair Infection Control Africa Network (ICAN)

Daniel Erwin
Replied at 11:49 AM, 13 Aug 2013

Dear Drs. Jensen, Mehtar and Nardell,

Thank you very much for your replies concerning shared anterooms. I have a follow-up question regarding anterooms in general, as I was surprised by Dr. Nardell's comment that "CDC does not generally encourage anterooms because of the difficulty in maintaining stepwise differential pressures so that they work properly."

The courses that I have taken (including the HSPH Building Design and Engineering Approaches to Airborne Infection Control) and reading CDC, ASHRAE, FGI etc. guidelines have led me to conclude that a dedicated anteroom is good idea because it helps buffer the transient pressure fluctuations that occur when staff enter and exit the AIIR, and this in turn helps maintain containment of any potentially infectious droplet nucli that might escape the AIIR during transient loss of the designed pressure relationships.

In a separate course on BSL-3 labs (which in principles works in a similar fashion to an AIIR equipped with an anteroom), the instructor (an engineer) emphasized that what matters most in the final analysis is that there is demonstrable continuous inward directional airflow: first through the anteroom door undercut into the anteroom, and second, through the patient isolation room door undercut into the AIIR. This is how containment of potentially infectious droplet nuclei is achieved. (note: this assumes the anteroom is slightly negative in relation to the hallway, and the AIIR is both negative in relation to the anteroom and in relation to the hallway). I've observed house staff with an attending take will over a minute to enter and exit an AIIR (with a patient on airborne infection precautions (AIP)) without an anteroom, during which time the negative pressure differential was lost and the pressure alarm was going off. It isn't possible to police this every time there is a patient on AIP.

In my experience, our facilities are able to reliably achieve the correct airflows and pressure relationships in a constant air volume (CAV) system. However, it should be verified daily by smoke trail testing whenever an AIIR is being used for AIP even when an equipped with an electronic manometer or other differential pressure indicator, because these devices can malfunction or fail. Where I see more variability is in the frequenty of quantitatively verifying volumetric airflow, pressure differentials and formal testing and balancing.

Perhaps Dr. Jensen could clarify the CDC's position on anterooms?

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