Transmission-based precautions is sort of a new term for us in dentistry. It's
something that's been used in hospital-based settings for many years. The
guideline on that was written in 2007. And it's for patients who are known or
suspected to be infected or colonized with infectious agents including, certain
epidemiological important pathogens that require additional control measures to
effectively prevent transmission. This is in addition to standard precautions and
this is the where we're going to spend the rest of this presentation — is talking
about these two other tiers of infection control precautions.
Transmission-based precautions actually include three different types of
transmission. One is contact, which we won't talk about today, because it's not
implicated in our current concern with COVID-19.
What I want to focus on are the other two tiers, which are droplet precautions and
airborne precautions. Droplet precautions are used for people who have a
respiratory illness, such as influenza, adenovirus, or SARS — and includes things,
such as using a face mask, even for exams. Whereas under standard precautions, we
would use a face mask if we were anticipating any generation of spatter
or spray, and then placing a face mask on the patient when they'll be in close
proximity to others. Airborne precautions which are the highest level or for
airborne pathogens such as tuberculosis chicken pox and measles one of the
things included with airborne precautions is isolation such as using
airborne infection isolation room, which I'll talk about a little bit more. Now
traditionally, because it's difficult and most dental offices are not
prepared to provide airborne precautions, it would be recommended that a dental
provider would delay treatment of patients who have these infections or
refer them to an appropriate facility who can treat them under isolation.
So what about this current virus the SARS Coronavirus 2 - that causes COVID-19?
Well generally the CDC recommends droplet precautions.
However, airborne precautions may be indicated if you're performing aerosol-generating
procedures — what they also call AGPs. A lot of the work that's been
done, and recommendations that have been made, have been based on the medical
research that was done after the SARS outbreak in 2003. During that outbreak — or
[...] retrospectively looking at that outbreak — they have found that airborne
transmission over a limited distance — say within a room — has been suggested though
not proven. And that's true of other infectious agents, such as influenza
virus and norovirus, which are primarily droplet transmitted diseases. So we're
going to talk a little bit about what all that means to us in dentistry.
First of all, droplet transmission is [...] respiratory droplets carrying infectious
pathogens that transmit infection when they travel directly from the
respiratory tract of the infectious individual to susceptible mucosal
surfaces of the surfaces of the recipient. So, for instance, when a person
who is infected with, in this case, COVID-19, coughs sneezes or speaks. And frankly,
even some breathing may release droplets that may be infected with virus,
that if they come into contact with another person's eyes nose or mouth, can
cause disease transmission. That's why they're currently recommending that we
wear face coverings if we're going to violate that 6-foot personal space for
social distancing. Because if we were to cough or sneeze, and we might be infected,
that could put other people at risk. Now, the other thing that we have to remember
is that these transmission based precautions were really developed with
hospital inpatient settings in mind. So we have to translate them for dentistry,
because things are a little different. So for — one of the main differences is when
they talk about the type of procedures that may create aerosols or droplets,
they generally are talking about medical procedures, such as endotracheal
intubation, extubation, cough-inducing procedures, CPR. Those are all things that
would require [...] droplet precautions and, under certain
circumstances, airborne. So in dentistry we can pretty much assume that it's for
any procedure that generates droplets of oral fluids [...] of an infected person.
Because we know that, if a person has COVID-19, the virus can be can be
isolated from their saliva. So the virus is present in saliva. And therefore,
when saliva is released there's a potential for exposure.
Now pathogens which are transmitted by the droplet route have not been
transmitted through the air over long distances. And that's because the
droplets are larger than an aerosol. They don't travel as far, and they fall to the
floor and other horizontal surfaces. Coronavirus is primarily transmitted
via droplet, but we're going to talk about why we may need to take airborne
precautions, as well. It's also important to understand the
difference between droplets and droplet nuclei. Droplets are usually considered
to be greater than five micrometers in size. Whereas droplet nuclei, which are
particles that arise from the desiccation of the suspended droplets,
can be smaller than five micrometers in size, which is a called the respirable range.
And those have been associated with airborne transmission.
Organisms transmitted by the droplet route don't remain infective over long
distances and, therefore, don't require things like, negative air pressure rooms.
But those that can be transmitted through aerosolization of droplet
nuclei are a different story. So just to recap with droplet
precautions, some of the strategies would be to place the patient
in a single room, the patient wears a mask any time they're outside of that
room, and providers wear a mask upon entering the room. So typically with
standard precautions you would put a mask on, you know, right before patient
treatment — and probably with the patient right there. In this case, you put it on
before you walk in the room. And, again, no special air handling, like negative air
pressure is required. And respirators are not required. And this would be for very
simple things, like talking, you know, If the patient has symptoms, you suspect
they may be ill, you put a mask on them. You talk about, you know, why you're going
to like, to defer treatment, and then send them home. This is not for providing
care that, would you say, a handpiece or anything else that might generate
aerosols, like an air water syringe. And finally, we get to airborne transmission.
This is the the highest tier on transmission-based precautions.
Dissemination of either airborne droplet nuclei or small particles that are in the
respirable size range — that's under five micrometers — and they contain infectious
agents that may remain infective over time and distance, such as spores of
Aspergillus and Mycobacterium tuberculosis. Examples of agents that are
also transmitted primarily by the airborne route, include tuberculosis the
rubeola virus that causes measles, and the varicella zoster virus that causes
Chickenpox.
This is not an area we've spent a lot of time on in
dentistry. So I think that it can cause a lot of confusion. And one of the things
that really helped me understand why we kind of straddle the line between
droplet precautions and airborne precautions when we talk about COVID-19
is this concept of the airborne transmission falling into three
different classifications of transmission route. The first being
obligate, where under natural conditions, disease occurs following transmission of
the agent only through inhalation of small particle aerosols, such as
tuberculosis, a true aerosol transmitted disease not transmitted by other means
such as contact with contaminated surfaces. And then there's the second
group, which are natural infections that result from transmission through
multiple routes. But small particle aerosols are the predominant route, such
as measles and varicella. They are really considered airborne transmission
diseases, but they could also be transmitted through droplet. And then
finally, there's opportunistic agents that naturally cause disease through
other routes. So they're not primarily airborne, but under special circumstances
they may be transmitted via fine particle aerosols. And this is where we
find SARS and, presumably, COVID-19. We'll know more, of course, as time goes on and
research is done. Also other respiratory illnesses, such as influenza, and also
norovirus and smallpox, are all considered opportunistic agents when it
comes to airborne transmission. Patients with confirmed, or persons under
investigation for suspected infection, with COVID-19, the recommendations are
that you would treat these patients under airborne precautions. And that
means the use of respirators, the use of airborne infection isolation rooms, and
other additional administrative and work practice controls, which I'll talk about
a little bit on the next slide. So in dentistry that really means if you have
a patient that you've screened and they say, you know, I've been told I have
COVID-19, or I'm being investigated for a suspected infection — perhaps they're in
quarantine because they've had an exposure — those patients should not be
seen in most dental settings, because we can't
provide these types of airborne precautions, and they could be referred
to an appropriate facility. One of the main components of airborne
precautions is the use of isolation rooms — and these airborne infection
isolation rooms are called AIIRs — have very specific requirements. It's not just
taking a private room and changing the air exchange and considering it a
isolation room. It has to have a specific number of air exchanges for new
construction. That would be twelve air exchanges per hour. It's allowed for
existing AIIRs to maintain six air exchanges per hour. There has to be a
[...] pressure differential between the room and the adjacent areas. So the
isolation room would have negative air pressure, which is achieved by having
only air exhaust from that room, and the only air intake would be the small
amount that comes in under the door. There also has to be monitoring of that
pressure differential. It has to be at a certain level in order to truly be
considered negative air pressure. Then that air that does exhaust can't be
recirculated within the building and potentially contaminate other rooms. it
has to exhaust to either the outdoors, or it can be exhausted through a HEPA
filter. Material for walls and floors has to be able to be cleaned and disinfected.
And there have to be signs on the room that restrict entry, so people know that
they can't walk into that room without proper PPE. And the door has to remain
closed.
[...]