Infection Control Today: Clinical Update


The Elusive Enemy:
Airborne Pathogens in Healthcare Facilities

By Kathy Dix

Airborne 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 person’s 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 contamination.”

Sinead Forkan-Kelly, nurse epidemiologist at Children’s Memorial Hospital in Chicago, finds these to be the most prevalent airborne pathogens:

  • 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 exhaust
  • 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

It’s 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 it’s more than that. You also have to protect employees of the hospital and the contractors who are in effect employees of the hospital. We’ve got to look at everybody there, and not be single-sighted.”

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 don’t stop and think about this: when you block all the air return, especially if you’re in a large construction zone, then you’re throwing the air handling equipment out of balance. The equipment knows it’s supposed to return a certain volume of air, and when it can’t return the volume it’s supposed to, it pulls additional air from other areas, and from seams and cracks in the duct work itself, so now you’re 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 didn’t rebalance the system to reflect the loss of volume coming from his space. Maybe the airflow resistance was such that it wasn’t 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 explains.

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 aren’t maintained properly, and in most hospitals I inspect, there’s a problem somewhere in the filtration system, either with filters that aren’t maintained properly, or that aren’t replaced as often as they should be replaced. There’s a frame that the filters are seated in, and if the frames are slightly dented or misaligned, the filter doesn’t seat as firmly as it should, and you get filter blowby or bypass, so air circulates around that and bypasses the filter,” says Draper.

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 don’t see it until you open up the wall cavity — you’re 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 we’re 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 we’re 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 we’ve 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 they’ll 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. “It’s clear that particularly in adolescents, pertussis is increasing in frequency around the country. It is a disease that remains difficult to diagnose, because physicians haven’t 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 don’t 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 that’s frequently been put aside in favor of PCR, but PCR is also not the world’s most sensitive test. Serologic testing is proposed, but at the moment there is only one approved serologic test and that’s 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 hasn’t been approved yet, and even so, a serologic test doesn’t have the immediacy.”

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 couldn’t 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 it’s 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. We’re ever more successful using strategies such as directly observed therapy, etc., and the campaign to eliminate TB, but it’s 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, we’re going to see immunization impact the epidemiology of varicella virus. We’ve 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. “That’s why we use both engineering controls and personal protective gear. Of course, the patient’s 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 don’t 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. That’s another reason to be vaccinated (with the influenza vaccine). There are three reasons beyond personal protection — the first is so you don’t give flu to patients. Many HCWs say, ‘I’ll stay home when I’m 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. That’s 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 don’t want to take flu home to your loved ones. Get flu shot or nasal spray vaccine; they’re 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. “That’s 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 it’s indicated, and that shows you how protective it can be, because I’ve had repeated exposures to some very infectious patients over the years. We like to quote football coach Vince Lombardi, who said, ‘It’s not sufficient to do the right thing most of the time. You’ve got to do the right thing all the time.’ Otherwise all the time, you expose yourself to potential infection.”

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