Infection Control Today: Clinical Update

August 1, 2005

The Elusive Enemy: Airborne Pathogens in Healthcare Facilities

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 pathogensthat 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 inwhich they can multiply inside, he says. In most cases, they becomeairborne by a persons coughing, talking, or sneezing. They can also betransmitted by touch through bodily fluids such as saliva, mucous, vomit, orfecal matter.

Hammes notes, We feel the most relevant protocols shouldinvolve HEPA filtration. However, we also feel that negative pressure should bemandatory for known cases. This is because patients in the nearby hall (who arenot wearing personal protective equipment) should also be protected from crosscontamination.

Sinead Forkan-Kelly, nurse epidemiologist at ChildrensMemorial Hospital in Chicago, finds these to be the most prevalent airbornepathogens:

  • 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 whohave been recently exposed to measles (rubeola) and/or chickenpox (varicella)and may potentially be contagious

  • Smallpox

  • Monkeypox

  • Severe AcuteRespiratory Syndrome (SARS)/coronavirus infection.

  • Avian influenza

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

Airborne particles can be widely dispersed by air currentsand may be inhaled by or deposited on the mucous membranes of a susceptiblehost. They are circulated through the ventilation system of the hospital withthe flow of air currents. We ventilate contaminated air out of the buildingthrough negative pressure. Negative pressure is maintained by keep double doorsclosed at the entrance of the room.

To prevent transmission of pathogens that may be spread byboth 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 forstaff, parents/guardians and visitors, says Forkan-Kelly. N95 personalrespirators, rather than standard isolation masks, are indicated for all staff,parents/guardians and visitors entering the room of a suspected or diagnosedcase of TB, SARS, smallpox, monkeypox, and avian influenza. A cleanmask/respirator is to be worn with each entry. Masks/respirators are to beremoved and discarded immediately upon leaving the room. Visiting is restrictedand allowed only under controlled assessment in consultation with infectionprevention and control department staff.

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

Fighting a Source

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

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

Another crucial point to remember is that when sealing offconstruction zones, often contractors will block off the air return vents toprevent dust and debris from entering the air return and being distributedthroughout the facility. That makes sense, but they dont stop and thinkabout this: when you block all the air return, especially if youre in a largeconstruction zone, then youre throwing the air handling equipment out ofbalance. The equipment knows its supposed to return a certain volume of air,and when it cant return the volume its supposed to, it pulls additionalair from other areas, and from seams and cracks in the duct work itself, so nowyoure 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 anddidnt rebalance the system to reflect the loss of volume coming from hisspace. Maybe the airflow resistance was such that it wasnt pulling air fromthere because it was pulling it through the return air vents, but now, like avacuum, this pipe is sucking in air from every little crack and crevice, heexplains.

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

Once this dust and any molds, bacteria, or other undesirablesreach the return air system, the system should mix the return air with freshair, heat or cool it, and then route it through a series of filters. Whatroutinely happens, though, is those filter banks and systems arent maintainedproperly, and in most hospitals I inspect, theres a problem somewhere in thefiltration system, either with filters that arent maintained properly, orthat arent replaced as often as they should be replaced. Theres a framethat the filters are seated in, and if the frames are slightly dented ormisaligned, the filter doesnt seat as firmly as it should, and you get filterblowby or bypass, so air circulates around that and bypasses the filter, saysDraper.

That air bypassing a filtration system could be dumped intoadjacent corridors, and the particles of dust can be picked up by the feet ofhealthcare workers or by tires on gurneys or wheelchairs and distributedthroughout the hospital. A lot of the spores associated with mold whichcan come out in the construction process, because a lot of the time the mold isinside 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 withmold that at least to some small degree was contained before theconstruction work.

The frightening aspect is spores resilience once theyare released, they demonstrate incredible resilience, and, Draper says, canlive 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 dispersethroughout the hospital and lie in wait] until moisture is delivered in the formof a mop, a leaky pipe, or even excessive humidity or window condensation, andthen they need a food source drywall paper/cellulose is a wonderful foodsource. We have to not allow those spores to escape the constructionarea 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 ofpreventive medicine at Vanderbilt University Medical Center in Nashville; chairof the infection control committee; and board member of the National Foundationfor Infectious Diseases. One is a very restrictive way airborne asopposed to droplet spread. In droplet spread, infectious agents are spread fromthe respiratory tract and usually spread only within three feet of anindividual. You can also get airborne spread, in which the pathogen gets intovery small particles that can actually circulate through air currents at greaterdistances, and some infectious agents can do both. Most of what we worry aboutin hospitals is droplet spread. The infection where were worried about bothdroplet and airborne spread is tuberculosis.

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

There is a possibility that healthcare institutions would havethe responsibility for providing the vaccine for HCWs if this is deemed anoccupational hazard, Schaffner says. They might also be responsible for keepingtrack of which employees accept and which decline, requiring an informeddeclination statement. Its clear that particularly in adolescents,pertussis is increasing in frequency around the country. It is a disease thatremains difficult to diagnose, because physicians havent seen it orconsidered the diagnosis, and it occurs in modified form in people who werepreviously immunized as a more subtle disease. The third conundrum with thediagnosis of pertussis is if a doctor has a candidate patient, it is in mostparts of the country difficult to diagnose, because we dont have readilyavailable diagnostic tests.

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

Another pathogen spread via droplets is influenza. HCWs cancertainly give influenza to patients, Schaffner confirms. And it is anational embarrassment that only about 38 percent of HCWs with patient contactavail themselves of influenza vaccine each year. My wife is not a medicalperson, but when she saw those statistics in the newspaper last year, she wasboth surprised and a bit indignant. She did not understand why it was not the professionalresponsibility of HCWs to be immunized for the sole reason of protectingpatients, so patients couldnt catch the flu from them. Her indignation isshared by many of us involved in infection control, occupational health, andpublic health. Increasingly, professional societies have been informing theirmembers that annual influenza immunization is the standard of professionalpractice for yourself, and is the ethical and medical thing to do. I think itsfair to say that we will see heightened interest by the Joint Commission on theAccreditation of Healthcare Organizations (JCAHO) in this subject. I hope thatthey will soon start to ask healthcare organizations to document their annualinfluenza immunization programs, document their results and display theirresults. Just by doing that, I think they will get the institutions moreassertively involved in providing influenza vaccine to their workers, andpersuading 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. Weare having greater success in pursuing its elimination, but with a largeproportion of the U.S. population being foreign-born the year 2000 censusindicated somewhere between 9 percent and 11 percent of people living in theUnited States today were born in another country people of foreign birth areeverywhere, and so we need to be aware of the possibility of tuberculosis. Wereever 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 onthe 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 poxexposures in the hospital. I think there are now over 30 states withrequirements that schoolchildren be immunized against chicken pox, soincreasingly, were going to see immunization impact the epidemiology ofvaricella virus. Weve seen the results of that, he adds.

Droplets are generally spread within three feet of an infectedpatient, so most of the risk to those of us who care for patients comes inthat immediate environment, where you get into the breathing zone of thepatient. 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 tooccur, Schaffner points out. Thats why we use both engineering controlsand personal protective gear. Of course, the patients illness or suspectillness has to be recognized before those engineering controls put the patientin an isolation room and personal protective equipment can be used effectively. Occasionally, you do get a patient whose tuberculosis issubtle 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, includinginfluenza. The CDC has introduced a cough etiquette program that was wonderfullywell accepted across the country, Schaffner says. We have cough and sneezestations throughout our institution, he adds. They are little stations with a sign on them remindingpeople about respiratory hygiene, with a box of facial tissues, and they remindpeople to cough into the tissue and discard it. We also have a handwashing gel available, and remind people towash their hands. If facial tissue is not available, we advise them to coughinto their sleeve. Not only have our patients responded to them, but somewhat toour surprise, our personnel use them. Patients really think we care about them and their families bydoing this.

This campaign dovetails with the hand hygiene campaign.However, there is still fine-tuning to be done in determining how sick is toosick to work. We dont want everyone with a sniffle or allergy or sinuscough to stay home, but they should stay home if they have influenza. I have totell you, we struggle with that annually. Thats another reason to bevaccinated (with the influenza vaccine). There are three reasons beyond personalprotection the first is so you dont give flu to patients. Many HCWs say,Ill stay home when Im sick. But after you get infected withinfluenza and before you yourself get sick,you can transmit the flu virus to patients and colleagues for a day or even twodays before you get sick. Thats a revelatory and empowering concept. No. 2, when influenza is in the community, we need you on thejob, 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 totake flu home to your loved ones. Get flu shot or nasal spray vaccine; theyreboth great, Schaffner says.

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