Infection Control Today: Clinical Update

August 1, 2005

The Elusive Enemy:
Airborne Pathogens in Healthcare Facilities

By Kathy Dix

pathogens in healthcare facilities remain elusive they can exist in
ventilation systems, within the walls, even in the plumbing. Certain pathogens
are more common than others, and some are frightening in their infectiousness.

The most prevalent airborne pathogens
that Frank Hammes, president of IQAir, sees include orthomyxovirus (influenza),
rhinovirus (colds), paramyxovirus (mumps), Streptococcus pneumoniae (pneumonia),
and corynebacteria diphtheria (diphtheria). These airborne pathogens must usually find a host body in
which they can multiply inside, he says. In most cases, they become
airborne by a persons coughing, talking, or sneezing. They can also be
transmitted by touch through bodily fluids such as saliva, mucous, vomit, or
fecal matter.

Hammes notes, We feel the most relevant protocols should
involve HEPA filtration. However, we also feel that negative pressure should be
mandatory for known cases. This is because patients in the nearby hall (who are
not wearing personal protective equipment) should also be protected from cross

Sinead Forkan-Kelly, nurse epidemiologist at Childrens
Memorial Hospital in Chicago, finds these to be the most prevalent airborne

  • Active pulmonary Mycobacterium tuberculosis (TB)
  • Active Varicella (chickenpox)
  • Disseminated Herpes zoster (Varicella)
  • Localized Herpes zoster with potential to disseminate in an immunocompromised/
    immune suppressed host
  • Active Rubeola (measles): Susceptible persons who
    have been recently exposed to measles (rubeola) and/or chickenpox (varicella)
    and may potentially be contagious
  • Smallpox
  • Monkeypox
  • Severe Acute
    Respiratory Syndrome (SARS)/coronavirus infection.
  • Avian influenza

Airborne transmission occurs by
dissemination of either airborne droplet nuclei (small-particle residue of
evaporated droplets that may remain suspended in the air for long periods of
time) or dust particles containing the infectious agent from the acts of
coughing, suctioning and cough producing procedures, sneezing, talking, etc. of
the infected person, Forkan-Kelly explains.

Airborne particles can be widely dispersed by air currents
and may be inhaled by or deposited on the mucous membranes of a susceptible
host. They are circulated through the ventilation system of the hospital with
the flow of air currents. We ventilate contaminated air out of the building
through negative pressure. Negative pressure is maintained by keep double doors
closed at the entrance of the room.

To prevent transmission of pathogens that may be spread by
both routes varicella, disseminated herpes zoster, and SARS, for example it
may be necessary to use a combination of airborne and contact isolation
precautions. Airborne transmission isolation procedure specifications require

  • A single-patient room with negative air pressure ventilation and outside
  • That the door to the room be kept closed except for entry and exit.

For all airborne diseases except TB, SARS, smallpox,
monkeypox, and avian influenza, standard isolation masks are indicated for
staff, parents/guardians and visitors, says Forkan-Kelly. N95 personal
respirators, rather than standard isolation masks, are indicated for all staff,
parents/guardians and visitors entering the room of a suspected or diagnosed
case of TB, SARS, smallpox, monkeypox, and avian influenza. A clean
mask/respirator is to be worn with each entry. Masks/respirators are to be
removed and discarded immediately upon leaving the room. Visiting is restricted
and allowed only under controlled assessment in consultation with infection
prevention and control department staff.

Forkan-Kelly also notes that movement and transportation of
the patient must be restricted to essential diagnostic/treatment purposes only.
These would be procedures that cannot be performed in the room, she
explains. Restrict patient and parents/ guardian from hallways,
common/community areas, playrooms, cafeteria, restaurants, and other public
areas in the hospital for the duration of isolation. For varicella cases, the
parents/guardian and visitors can be evaluated for immunity to allow less
restricted movement. Coordinate such necessary trips with the receiving
department to times of the day during which other patients in the area are not
present if possible. Provide the patient with a well-fitted standard isolation
mask, clean gown, and linen for transport and for the procedure. And use
additional barriers of gowns, gloves, protective eyewear, and hand hygiene per
standard/universal precautions and hand hygiene policies.

Fighting a Source

Its not just pathogens that are a concern, points out Al
Draper, MS, director of restoration for LVI Services Inc. Draper has worked as a
toxicologist, an industrial hygienist, and in the construction field for more than 25
years. Common things in the air are construction dust, wood dust, and drywall
dust. Those are not pathogens, but they are definitely respiratory irritants,
and certain types of dust can be used as food sources for other airborne
irritants like molds and bacteria, he says.

What people sometimes fail to know and is one of the
big holes when it comes to doing infection control in hospitals is not
overly controlling the work zone, adds Draper. It is necessary to isolate the
work zone, and negative pressure is also recommended. However, The problem with this is sometimes contractors get
carried away, and if they use too much negative pressure, they can actually drag
pathogens from adjacent spaces that are not within the construction project
like a waste disposal area nearby, an ER or an isolation ward and by
creating this negative pressure, they can be exposing the people within the work
zone or the construction workers to infectious items. People get blinders on.
When they hear infection control, they always think, We have to protect the
patient from the contractor, but its more than that. You also have to
protect employees of the hospital and the contractors who are in effect
employees of the hospital. Weve got to look at everybody there, and not be

Another crucial point to remember is that when sealing off
construction zones, often contractors will block off the air return vents to
prevent dust and debris from entering the air return and being distributed
throughout the facility. That makes sense, but they dont stop and think
about this: when you block all the air return, especially if youre in a large
construction zone, then youre throwing the air handling equipment out of
balance. The equipment knows its supposed to return a certain volume of air,
and when it cant return the volume its supposed to, it pulls additional
air from other areas, and from seams and cracks in the duct work itself, so now
youre dragging in air from who-knows-where in a dirty old ceiling somewhere,
because the contractor did such a good job blocking off the return air vents and
didnt rebalance the system to reflect the loss of volume coming from his
space. Maybe the airflow resistance was such that it wasnt pulling air from
there because it was pulling it through the return air vents, but now, like a
vacuum, this pipe is sucking in air from every little crack and crevice, he

The solution involves rebalancing the system, informing the
maintenance engineers and HVAC control systems staff that the computerized
system needs to be rebalanced to reflect the revised air volume.

Once this dust and any molds, bacteria, or other undesirables
reach the return air system, the system should mix the return air with fresh
air, heat or cool it, and then route it through a series of filters. What
routinely happens, though, is those filter banks and systems arent maintained
properly, and in most hospitals I inspect, theres a problem somewhere in the
filtration system, either with filters that arent maintained properly, or
that arent replaced as often as they should be replaced. Theres a frame
that the filters are seated in, and if the frames are slightly dented or
misaligned, the filter doesnt seat as firmly as it should, and you get filter
blowby or bypass, so air circulates around that and bypasses the filter, says

That air bypassing a filtration system could be dumped into
adjacent corridors, and the particles of dust can be picked up by the feet of
healthcare workers or by tires on gurneys or wheelchairs and distributed
throughout the hospital. A lot of the spores associated with mold which
can come out in the construction process, because a lot of the time the mold is
inside the wall, and you dont see it until you open up the wall cavity
youre really causing an exposure once you begin the construction effort with
mold that at least to some small degree was contained before the
construction work.

The frightening aspect is spores resilience once they
are released, they demonstrate incredible resilience, and, Draper says, can
live for years or even hundreds of years in a dormant state just like a seed,
until they have two things moisture and some food source. [They disperse
throughout the hospital and lie in wait] until moisture is delivered in the form
of a mop, a leaky pipe, or even excessive humidity or window condensation, and
then they need a food source drywall paper/cellulose is a wonderful food
source. We have to not allow those spores to escape the construction
area or were basically seeding the hospital with future mold problems, he concludes.

Droplet vs. Airborne Spread

We can think about airborne pathogens in two ways,
explains William Schaffner, MD, professor and chair of the department of
preventive medicine at Vanderbilt University Medical Center in Nashville; chair
of the infection control committee; and board member of the National Foundation
for Infectious Diseases. One is a very restrictive way airborne as
opposed to droplet spread. In droplet spread, infectious agents are spread from
the respiratory tract and usually spread only within three feet of an
individual. You can also get airborne spread, in which the pathogen gets into
very small particles that can actually circulate through air currents at greater
distances, and some infectious agents can do both. Most of what we worry about
in hospitals is droplet spread. The infection where were worried about both
droplet and airborne spread is tuberculosis.

Two other pathogens include varicella and pertussis. In our
neck of the woods, pertussis has become the most common healthcare exposure, or
potential exposure, that our occupational health service has to contend with,
Schaffner declares. It exceeds needlesticks and tuberculosis. The Centers for
Disease Control and Prevention (CDC) is interested in doing a survey to see
exactly how commonly pertussis or presumed pertussis exposures are occurring,
and how often prophylaxis is being administered and the like. This is
particularly germane because weve just had licensed an acellular pertussis
vaccine and another one is anticipated to be used as a booster dose in
adolescents and adults. The CDC Advisory Committee on Immunization Practices
(ACIP) will be considering very soon recommendations for the use of acellular
vaccine in adults, and one of the populations theyll be looking at is
healthcare workers (HCWs). The question will come up: Should all or some HCWs routinely be
offered an acellular booster because of occupational circumstances?

There is a possibility that healthcare institutions would have
the responsibility for providing the vaccine for HCWs if this is deemed an
occupational hazard, Schaffner says. They might also be responsible for keeping
track of which employees accept and which decline, requiring an informed
declination statement. Its clear that particularly in adolescents,
pertussis is increasing in frequency around the country. It is a disease that
remains difficult to diagnose, because physicians havent seen it or
considered the diagnosis, and it occurs in modified form in people who were
previously immunized as a more subtle disease. The third conundrum with the
diagnosis of pertussis is if a doctor has a candidate patient, it is in most
parts of the country difficult to diagnose, because we dont have readily
available diagnostic tests.

Schaffner continues, We have readily available culture. We
have PCR, which I think is not approved yet by the FDA as a diagnostic test, but
by the time doctors think about [pertussis as the cause], after two weeks of cough, cultures are frequently negative. The same
can be said for direct fluorescent antibody (DFA) testing, and thats
frequently been put aside in favor of PCR, but PCR is also not the worlds
most sensitive test. Serologic testing is proposed, but at the moment there is
only one approved serologic test and thats available from the health
department in Massachusetts and nowhere else. There are applications into the
FDA to provide licensed testing, licensure for testing serologically, but that
hasnt been approved yet, and even so, a serologic test doesnt have the

Another pathogen spread via droplets is influenza. HCWs can
certainly give influenza to patients, Schaffner confirms. And it is a
national embarrassment that only about 38 percent of HCWs with patient contact
avail themselves of influenza vaccine each year. My wife is not a medical
person, but when she saw those statistics in the newspaper last year, she was
both surprised and a bit indignant. She did not understand why it was not the professional
responsibility of HCWs to be immunized for the sole reason of protecting
patients, so patients couldnt catch the flu from them. Her indignation is
shared by many of us involved in infection control, occupational health, and
public health. Increasingly, professional societies have been informing their
members that annual influenza immunization is the standard of professional
practice for yourself, and is the ethical and medical thing to do. I think its
fair to say that we will see heightened interest by the Joint Commission on the
Accreditation of Healthcare Organizations (JCAHO) in this subject. I hope that
they will soon start to ask healthcare organizations to document their annual
influenza immunization programs, document their results and display their
results. Just by doing that, I think they will get the institutions more
assertively involved in providing influenza vaccine to their workers, and
persuading HCWs to actually take the vaccine.

Tuberculosis (TB) is a continuing cause of concern as well.
Tuberculosis is not gone; it is being imported, reports Schaffner. We
are having greater success in pursuing its elimination, but with a large
proportion of the U.S. population being foreign-born the year 2000 census
indicated somewhere between 9 percent and 11 percent of people living in the
United States today were born in another country people of foreign birth are
everywhere, and so we need to be aware of the possibility of tuberculosis. Were
ever more successful using strategies such as directly observed therapy, etc.,
and the campaign to eliminate TB, but its not gone yet and is very much on
the list of respiratory infections to be concerned about.

Schaffner continues, The last one, which is not gone yet,
is chicken pox. Chicken pox is profoundly reduced in many parts of country,
because of active immunization programs, but we continue to have chicken pox
exposures in the hospital. I think there are now over 30 states with
requirements that schoolchildren be immunized against chicken pox, so
increasingly, were going to see immunization impact the epidemiology of
varicella virus. Weve seen the results of that, he adds.

Droplets are generally spread within three feet of an infected
patient, so most of the risk to those of us who care for patients comes in
that immediate environment, where you get into the breathing zone of the
patient. Or you put the patient in your breathing zone if you have influenza,
and the more time you spend in that zone, the more likely transmission is to
occur, Schaffner points out. Thats why we use both engineering controls
and personal protective gear. Of course, the patients illness or suspect
illness has to be recognized before those engineering controls put the patient
in an isolation room and personal protective equipment can be used effectively. Occasionally, you do get a patient whose tuberculosis is
subtle and is not suspected immediately, and the patient has been in the hospital for three days not on isolation.

Cough etiquette is one of the most important (and most simple)
methods of preventing the spread of common respiratory pathogens, including
influenza. The CDC has introduced a cough etiquette program that was wonderfully
well accepted across the country, Schaffner says. We have cough and sneeze
stations throughout our institution, he adds. They are little stations with a sign on them reminding
people about respiratory hygiene, with a box of facial tissues, and they remind
people to cough into the tissue and discard it. We also have a handwashing gel available, and remind people to
wash their hands. If facial tissue is not available, we advise them to cough
into their sleeve. Not only have our patients responded to them, but somewhat to
our surprise, our personnel use them. Patients really think we care about them and their families by
doing this.

This campaign dovetails with the hand hygiene campaign.
However, there is still fine-tuning to be done in determining how sick is too
sick to work. We dont want everyone with a sniffle or allergy or sinus
cough to stay home, but they should stay home if they have influenza. I have to
tell you, we struggle with that annually. Thats another reason to be
vaccinated (with the influenza vaccine). There are three reasons beyond personal
protection the first is so you dont give flu to patients. Many HCWs say,
Ill stay home when Im sick. But after you get infected with
influenza and before you yourself get sick,
you can transmit the flu virus to patients and colleagues for a day or even two
days before you get sick. Thats a revelatory and empowering concept. No. 2, when influenza is in the community, we need you on the
job, not at home being a patient yourself. In this era of nursing shortages,
etc., we need every able-bodied healthcare worker. Third, you dont want to
take flu home to your loved ones. Get flu shot or nasal spray vaccine; theyre
both great, Schaffner says.

Genuine airborne outbreaks not outbreaks due to droplet
spread are extremely unusual; there are such outbreaks, but the more common
spread of respiratory pathogens is via the droplet route. When you have
outbreaks (for example, clusters of TB transmission), they are almost always to
people who have had substantial close-in unprotected contact with the patient,
Schaffner points out. Thats important, because it enables you with the
appropriate diagnosis with an isolation room and good training and use of
respirators, to really protect other patients, visitors, the incidental
physician and healthcare workers as well as people going into the room having
close and prolonged contact with the patient. If you apply those rigorous
control procedures, and do it in a rigorous fashion, you can interrupt
transmission. I as an infectious disease physician have cared for people with
tuberculosis throughout my professional career, but I still have a negative TB
test. That is because I am obsessive about the use of my respirator when its
indicated, and that shows you how protective it can be, because Ive had
repeated exposures to some very infectious patients over the years. We like to
quote football coach Vince Lombardi, who said, Its not sufficient to do
the right thing most of the time. Youve got to do the right thing all the
time. Otherwise all the time, you expose yourself to potential infection.