HVAC And Infectious Diseases

May 13, 2004
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[Editor's note: This is the first installment of a three-part series on the role of HVAC in today's health care environments. This article focuses on ways to minimize the spread of emerging infectious diseases, bioweapons, and other high-impact agents.]

TAMPA, Fla. - Now more than ever, the risks of emerging infectious diseases, pandemics, and biological weapons place a heavy burden on hospital administrators and their mechanical operations staff, including mechanical systems subcontractors.

Contractors may not need to know the full etiology, but in order to work effectively in the hospital and health care market, they need knowledge of these diseases, plus pressurized isolation space techniques and ultraviolet germicidal irradiation (UVGI) methods.

This was the general consensus from a session on Emerging Infectious Diseases, part of the 2004 IAQ Conference co-sponsored by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and the American Society for Healthcare Engineering (ASHE), which took place in Tampa this spring.

What's That In The Air?

"Environmental opportunistic infections" are developing faster than ever before, pointed out Andrew Streifel, University of Minnesota hospital environmental specialist, Minneapolis/St. Paul.

An opportunistic infection can be relatively harmless in a healthy person - that is, it may cause symptoms, but the body's immune system is able to fight it.

However, it could cause severe problems, even death, for people whose immune systems are weakened or compromised, Streifel explained. These people include those undergoing chemotherapy, which essentially shuts down the immune system, and people with certain illnesses that work directly on the immune system, such as AIDS. Also at greater risk are the very young, whose immune systems are still developing, and the old, whose immune systems are starting to decline.

At least equally troubling are the strains of drug-resistant infections that have developed because of advanced antibiotics and their overprescription, Streifel said. Their spread is increased due to globalization and travel, which can increase the spread of infectious illness to pandemic proportions.

Then there are bioweapons, which can be responsible for airborne-spread microbials and toxins. The mode of spread is primarily through the air and water.

Human infectious agents can include tuberculosis (TB), chicken pox, herpes zoster, measles, smallpox, monkey pox, and severe acute respiratory syndrome (SARS).

Stopping the spread of such diseases requires isolation, and possibly negative-pressure, airborne-infection isolation rooms, said Streifel.

Fungi are another airborne cause of illness for hospital staff and patients alike. One of the most problematic, according to Streifel, is aspergillus, which can be released in large amounts when building renovations take place. "Ongoing destruction and demolition releases bursts of aerosols," he said.

It doesn't require something as dramatic as renovation to release aerosols, Streifel continued.

"Fancoil insulation, for in-stance, can be disturbed and distributed through maintenance."

Air Pressurization

Streifel pointed out that there are several things to keep in mind when designing or working with negative-pressure isolation rooms or areas.

  • Don't cut corners if you're going to use a portable HEPA filter in a negative-pressure isolation room. "You can't go on the cheap," he said.

  • Be careful to ensure that exhaust air from such an area blows out of the building rather than entering into the hospital's total ventilation system. For this purpose, consider using a portable, negative-pressure anteroom to prevent contaminants from being drawn out when the room's door is opened.

  • Make sure maintenance administration and training are supported with on-site documentation.

  • Verify ventilation parameters. For testing, use the proper equipment (i.e., air balance hood and micromanometer).

  • "Filtration works when it's properly installed and maintained," Streifel said. However, this is not being done, at least not often enough. He also indicated frustration that all air filters currently are tested in labs, so their ratings do not reflect real-world results. Low-pressure-drop HEPA filters are good products, he said.

  • Make use of mechanical and natural zones.

  • Understand control issues.

  • Maintain the system to de-sign criteria.

  • Train employees on the system's operation and maintenance.

    Bioweapons

    Information on intentionally caused infections is critical for the designers, installers, and servicers of today's hospital mechanical systems, according to Lewis Radonovich, M.D., of the Center for Biosecurity, University of Pittsburgh, who spoke on "Buildings and the Threat of Bioweapons."

    He started by reviewing the anthrax threat case on Capitol Hill in 2001, when Sen. Tom Daschle's office received contaminated mail that tested positive for anthrax spores. The HVAC system was turned off in 45 minutes, which Radonovich said is pretty good for a government building. "There is a single ventilation system for nine floors in the southeast quadrant," he said. In this case, 28 out of 442 people in the building that day had positive anthrax swabs.

    The postal worker who handled the letter became ill, dying of an overwhelming anthrax infection in just a few days. Radonovich showed X-rays of this worker's lungs, documenting the shockingly rapid spread of the disease.

    In all of 2001 there were 22 total cases of anthrax related to bioterrorism, including five deaths.

    The bioweapons threat, he continued, is "appealing to terrorists because it is accessible and disruptive." The advancement of bioscience is tied to the current bioweapons threat.

    There also are risks of "recharge" thinking; "It worked here, so we'll attack somewhere else, too," Radonovich explained.

    If 100 kg of anthrax were to be released over Washington, "it would result in deaths comparable to a 1-Megaton nuclear bomb," he stated.

    Radonovich went on to say that the mass production of bioweapons is fairly easily concealed. There also is an existing knowledge base. "Soviet bioweapons ... employed over 60,000 people in the 1980s."

    High-Impact Agents

    Class A agents have a high public health impact. "Anthrax and smallpox are on the top of the list," he said. "Anthrax is widely accessible, harvested from the soil. In the absence of UV light, anthrax can live indefinitely."

    Physicians are often relatively slow to detect these agents because the symptoms they create can mimic a host of other ailments that must be first ruled out through testing. Anthrax treatment can be complicated, requiring 40 to 63 days on antibiotics. Decontamination is expensive, and preventatives are limited.

    "We're very scared of the possibility of smallpox being released," Radonovich said. Such an event would have "enormous consequences."

    Smallpox is particularly dangerous because of its person-to-person transmission and high mortality rate. There currently is no treatment, and even the vaccine has complications. "If there is one case [of smallpox] anywhere in the world, it will be a global health problem." It probably would be released as an aerosol, he said.

    Thanks to sophisticated HVAC systems, he said, "something can be done about this."

    A New Place For UVGI?

    Michael R. Strommen, Ph.D., is an atmospheric chemist with 3M, St. Paul, Minn. His talk titled "Characteristics and Control of Airborne Microorganisms - Airborne Particle Characteristics" had some graphics that looked like a major airline's flight trajectories.

    These showed the movement of spores and other particles in-side a room. Computer modeling showed movements with various hospital room configurations.

    "Spores can be transmitted in the air," he said. Some infectious diseases, like TB, are transmitted in droplet nuclei. "Viruses on rare occasions seem to be transmitted through the air," he said.

    For particle filtration, he recommended putting nonwoven media in the path of the airstream. These filters should have synthetic and glass fibers. "There is a critical need to ensure the integrity of the filter seal," he said.

    He also noted that most particles wind up hitting the upper areas of walls. Because of this, he suggested that the mechanical and IAQ industries look at ways to place UVGI units to take advantage of this natural movement. Installing them on upper wall areas or in the ceilings of special areas, like surgical suites, isolation rooms, and bone marrow transplant areas - all of which need extremely clean conditions - could be more beneficial, he said, than more traditional UVGI placement at the air-handling unit coils as long as care is taken to protect the patients.

    Publication date: 05/17/2004

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