SARS: The Facts Air Filter Professionals Should Know

SARS users in a new world of challenges

The world of Jules Verne, described 130 years ago in Around the World in 80 Days, was one where many died from infectious diseases. Consumption (TB), syphilis, pneumonia, and gangrene claimed lives now saved by antibiotics and prevention. Railroads and steamships soon made the world small enough for outbreaks of “the Asian flu” to occur with infrequent regularity. A short 130years later, modern transportation and commerce have led to a dramatically changed situation. “Sick-building syndrome,” Legionella, AIDS/HIV infection, Ebola virus, and West Nile virus became sudden and serious topics. Within just the past 3 years, the“post-9/11” era threats of anthrax and other bioterrorism have joined to narrow our perspectives.

And now comes SARS – Severe Acute Respiratory Syndrome

Fact #1 – What Is SARS?

SARS appears to be caused by a corona virus, so named because of the “halo” or “crown-like” appearance around particles viewed by an electron microscope. First isolated from chickens in 1937, the (15 or so?) known corona viruses infect man but also cattle, pigs, rodents, cats, dogs, and birds. Corona viruses have a single-strand of RNA, the longest found in any RNA-type virus. Genetic sequencing has not yet provided any clues to designing a vaccine. Reinfections occur throughout life, so the prospects for effective immunization appear bleak. Opportunistic co-infections by other viruses might contribute to rapid and easy mutation of the corona virus and to a higher death rate.

Fact #2 – How Is It Spread?

Outbreaks of this emerging viral “pneumonia” in several countries appear traceable to exposures to fellow travelers with later spread within families, health care workers, and other close contacts. Thanks to modern jet travel, a business traveler now can, within 80 hours, hold meetings (and expose hundreds of contacts) on 6 continents and arrive innocently back home before symptoms appear. The “game” most certainly has changed and the stakes are potentially deadly. The exponential value of such contacts makes the amount of potential exposure immeasurable and challenging to contain.

SARS is both simple and complicated. Simple in the sense of recognizing symptoms – fever (often high), headache, malaise, muscle aches, mild respiratory symptoms, then later development of a dry nonproductive cough, shortness of breath, even lowered blood oxygen. At this writing, the death rate approaches 5%. SARS is complicated in the sense of determining a cause, finding a cure, and controlling outbreaks. The majority of patients have been adults aged 25 to 70 years who were previously healthy; few cases have been found in children under 16 years old. Typical incubation appears to be 2 to 7 days, though periods up to 10 days have been suggested. Viral shedding (promoting infection of others) apparently can occur for 10 to 20 days, perhaps longer.

Fact #3 Is This SARS Outbreak Something New?

Is this a recombination between human and animal virus or is this an animal virus now attacking humans? The answer is not yet known. The SARS agent, as genetically sequenced in April, is a novel corona virus that has not previously been present in humans. This might be the first example of a corona virus causing severe disease in humans. What is known is that developing countries have large human populations, often living in close contact with large animal populations used for food and farming. Unlike our “clean” society, many of these people endure marginal sanitation, rampant malnutrition, and minimal access to medical care. Detection of corona virus in the feces of kittens in the quarantined Hong Kong apartments raises the specter that domestic pets (or commercial animals) might serve as non-symptomatic hosts, creating worldwide reservoirs of SARS that might never be eliminated. Such large population reservoirs are fertile breeding grounds for mutation of bacteria and viruses, experienced commonly as “the Asian flu.” Corona virus infection is very common, occurs worldwide, and has a seasonal prevalence in winter.

Fact #4 How Is It Controlled?

The implications for control of the SARS epidemic, to prevent a pandemic, are ominous. Corona viruses in humans have been found to cause respiratory infections commonly (including SARS), enteric (gut) infections occasionally, and even neurological syndromes (rarely). Investigators recently documented SARS viral particles in stool samples. The finding of fecal contamination strongly suggests that poor sanitation, hand-to-hand and hand-to-mouth contact, and even fomite transfer (spread of infection present on inanimate objects which do not support their growth, such as plumbing fixtures, towels, and toilets) must be monitored.

The well-accepted vectors of airborne droplets (produced by coughing and sneezing), direct contact with secretions or droplets (nose, mouth, eyes, skin), and personal-environment fomite objects (bedrails and bedside furnishings, personal articles, plumbing fixtures, towels, bed linens, and clothing) – as encountered with “the common cold” – have led to recommendations from the U. S. Centers for Disease Control for isolation infection control precautions and potential quarantine. Current recommendations suggest that a diluted household bleach solution (1:50 or perhaps 1:100) might assist with immediate local disinfection of a sickroom. And common-sense precautions for “common cold” exposures still make sense – adequate rest and nutrition, avoidance of smoking, frequent hand-washing, good personal hygiene, covering nose and mouth when sneezing or coughing, separate utensils and towels, good indoor ventilation, and avoidance of crowded places with poor ventilation. Wearing “surgical” masks or N95 masks might provide some obvious protection as well.

Fact #5 – What About HVAC and Filtration?

If one exposure route of SARS is airborne, what implications does this fact have for HVAC systems, not only filtration but also ductwork? If airborne droplets settle onto and can spread from floors, walls, furnishings, light fixtures, and even window drapes, what implications does this fact have for remediation or disposal of furnishings before remediation of the actual room structure? Cleaning an infected area poses special issues with regard to corona virus decontamination. At present, most recommendations are for adherence to hospital infection control manuals, such as would be used for hepatitis virus. We expect that further experience with the SARS agent will lead to specific standards that will give the highest degree of assurance to the community. Serological testing (detecting antibodies against the virus) and molecular testing (for virus genetic material) involve fluids from an infected patient. As yet, no “swabs” from an environmental object (floor, fixture, duct) or air-sample plates or filters can detect viral presence. Airborne human corona virus particles appear to survive dramatically longer in lower temperature/higher relative humidity conditions.


SARS creates a whole new world for all of us, not just indoor environmental quality professionals. But the rest of our world will be looking to us to assure them of clean and healthy indoor air quality. SARS, in itself, might be a short-lived “event.” But the prospect remains that we may just be seeing the tip of the iceberg – the tip with regard to the spread of SARS or (and more ominously)the tip with regard to a ushering in a new era, with ready development and easy spread of “common infections worldwide,” bringing severe complications or deadly outcomes. Whatever the scenario, we need to begin adopting perspectives that will enable us to address these challenges squarely and successfully.

SARS: The Facts; Summer 2003 issue of Air Media
Author(s): John Parks Trowbridge M.D., FACAM; Skiter Kowalski, CIE, CAFS, CMR PIAQMsm, AQM Consultants