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September 2009
Inside This Issue
Flu Season is Here
From the Center on Disease Control
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World Energy Engineering Congress
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With all the talk about Swine Flu, we thought this would be a good time to provide some scientific information about influenza viruses and how they are transmitted.  Although airborne aerosols represent only one of the three ways in which viruses are transmitted, it is helpful to understand that good IAQ can address one third of the equation.
Carl Mitchell, Vice-President Sales
cmitchell@DynamicAQS.com
Flu Season is Here

Products from Dynamic Air Quality Solutions can trap and destroy flu viruses including the H1N1 Swine Flu Virus

With flu season upon us, there is no better time to talk about IAQ.  Obviously, there has been a lot of talk about Swine Flu.  We thought it might be helpful to cover some of the basics.  Viruses are tiny organisms -smaller than 0.1 microns.  However, in their spread, they are generally part of a larger particle.  H1N1 or Swine Flu is spread in the same fashion as ordinary influenza.   There are three basic mechanisms of transmission:

1) Large Droplet Transmission:  Here droplets containing the flu virus and greater than 5 microns are coughed or sneezed out by someone with the flu.  These are immediately inhaled or otherwise ingested by someone in close proximity.  These droplets do not stay airborne for more than 15 to 30 seconds and then can also settle onto surfaces, which can lead to ...

2) Surface transmission:  Here flu viruses are passed from the nose, mouth, or hand to a surface (such as a door knob, hand rail, counter top, etc.) that is then touched by someone else.  This person then touches his or her eyes, nose or mouth and the virus is given a path in.  Flu viruses can live on a hard surface for up to 24 hours and on a soft surface for around 20 minutes

3) Aerosol or airborne transmission:  Here droplets smaller than 5 microns (many smaller than 1.5 micron) stay suspended in the air for indefinite periods of time.  They can then be inhaled deep into the lungs and plant the infection.

The relative impact of each of these is very hard to define. But all three play an important role.  Air cleaners in a central system can help primarily in the case of airborne transmission, where the virus can be airborne for hours or days.   Whether an air cleaner can remove influenza virus, such as Swine Flu, from the air, depends on the type of air cleaning technology. 

HEPA filtration is effective at removing particles from the air that are 0.3 microns or larger in size.  It will also do fairly well on particles smaller than that, but, to be effective, it would need to be full flow.  Because of static, size, and cost constraints, this is not an option for many HVAC systems.  Dynamic Air Cleaners are also an effective way to get into the sub-micron range and are compatible with the limitations of smaller equipment.  Dynamic's commercial air cleaners are used in many hospital applications.  Passive filters that are greater than MERV 13 should be somewhat helpful as well in capturing particles in the size range of concern.

Air purifiers incorporating UV lamps expose the air passing through them to ultra violet light which does kill airborne viruses without otherwise impacting the environment.  The key for UVC to be effective is contact time with the lamp.  This can be hard to ensure when the air is moving at 500-1,000 feet per minute down a duct.  The Dynamic RS-3 addresses this issue by capturing the pathogens on a translucent media and repeatedly exposing them to high intensity UVC.  The RS-3 incorporates one inch Dynamic Air Cleaners and a high-output UVC lamp.  Behind the lamp is an oscillating parabolic reflector that focuses the lamp into a sterilizing beam that constant sweeps the media.  The pathogens are caught on the media and the lamp inactivates them.

UV air purifiers that also use TiO2 technology (such as the Dynamic Advanced PCO) can amplify the UV to make sterilization even more effective.   Where there is not space for the RS-3, coupling a one inch Dynamic Air Cleaner with a Dynamic Advanced PCO System is a powerful combination.

Beware of systems that rely on Ozone, such as ionizers, plasma ionizers and ozone generators. While Ozone can inactivate pathogens, the ambient level necessary for it to do so would be hazardous to the occupants of the space.

As for protecting yourself from large droplet and surface transmission, here are some tips for protecting yourself and others from airborne viruses, such as Swine Flu:
  • Cover your nose and mouth with your sleeve or a tissue when coughing or sneezing.
  • Dispose of dirty tissues promptly and carefully.
  • Wash hands frequently with soap and water to reduce the spread of the virus from your hands to face, or to other people.
  • Clean hard surfaces frequently, such as door handles, using normal cleaning products.
IAQ products such as those available from Dynamic Air Quality Solutions can help reduce the risk of transmitting viruses such as the H1N1 Swine Flu virus, but no IAQ products (or for that matter any other kind of product) will afford complete protection.  In short, cleaning your hands, cleaning your surfaces, and cleaning your air, are the best precautions you can take.
From the Center on Disease Control

The following information has been excerpted from a 2006 article published by the CDC entitled Review of Aerosol Transmission of Influenza A Virus.  To view the entire paper, click here.
 
Influenza viruses can be transmitted through aerosols, large droplets, or direct contact with secretions. These 3 modes are not mutually exclusive.  Published evidence indicates that aerosol transmission of influenza can be an important mode of transmission, which has obvious implications for pandemic influenza planning:
 
Influenza Virus Aerosols
By definition, aerosols are suspensions in air (or in a gas) of solid or liquid particles, small enough that they remain airborne for prolonged periods because of their low settling velocity. Settling times (for a 3 meter fall) for specific diameters are 10 seconds for 100 microns, 4 min for 20 microns, 17 min for 10 microns, and 62 min for 5 microns; particles with a diameter <3 microns essentially do not settle. Settling times can be further affected by air turbulence.
 
The median diameters at which particles exhibit aerosol behavior also correspond to the sizes at which they are efficiently deposited in the lower respiratory tract when inhaled. Particles of >6 microns in diameter are trapped increasingly in the upper respiratory tract; no substantial deposition in the lower respiratory tract occurs at >20 microns. Many authors adopt a size cutoff of <5 microns for aerosols.
 
Coughing or sneezing generates a substantial quantity of particles, a large number of which are <5-10 microns in diameter. In addition, particles expelled by coughing or sneezing rapidly shrink in size by evaporation, thereby increasing the number of particles that behave as aerosols. Particles shrunken by evaporation are referred to as droplet nuclei. This phenomenon affects particles with a diameter at emission of <20 microns, and complete desiccation would decrease the diameter to a little less than half the initial diameter. Droplet nuclei are hygroscopic. When exposed to humid air (as in the lungs), they will swell back. One would expect that inhaled hygroscopic particles would be retained in the lower respiratory tract with greater efficiency, and this hypothesis has been confirmed experimentally. Because aerosols remain airborne, they can be carried over large distances, which may create a potential for long-range infections.  The occurrence of long-range infections is affected by several other factors. These include dilution, the infectious dose, the amount of infectious particles produced, the duration of shedding of the infectious agent, and the persistence of the agent in the environment. Inferring an absence of aerosols because long-range infections are not frequently observed is incorrect.
 
Humans acutely infected with influenza A virus have a high virus titer [concentration] in their respiratory secretions, which will be aerosolized when the patient sneezes or coughs. The viral titer measured in nasopharyngeal washes culminates on approximately day 2 or 3 after infection.  The persistence of the infectivity of influenza virus in aerosols has been studied in the laboratory. In experiments that used homogeneous aerosolized influenza virus suspensions (mean diameter 6 microns), virus infectivity at a fixed relative humidity undergoes an exponential decay; this decay is characterized by very low death rate constants, provided that the relative humidity was in the low range of 15%-40%.  These results are consistent with those of an older study (admittedly performed in a more rudimentary manner) in which infectious influenza viruses in an aerosol could be demonstrated for up to 24 hours by using infection in mice as a detection method, provided that the relative humidity was 17%−24%. In all these studies, the decay of virus infectivity increased rapidly at relative humidity >40%.  The increased survival of influenza virus in aerosols at low relative humidity has been suggested as a factor that accounts for the seasonality of influenza. The sharply increased decay of infectivity at high humidity has also been observed for other enveloped viruses.
 
Experimental Influenza Infection
Additional data from experiments conducted with aerosolized influenza virus (average diameter 1.5 microns) showed that when a dose of 3 TCID50 was inhaled, ≈1 TCID50 only was deposited in the nose. Since the dose deposited in the nose is largely below the minimal dose required by intranasal inoculation, this would indicate that the preferred site of infection initiation during aerosol inoculation is the lower respiratory tract. Another relevant observation is that whereas the clinical symptoms initiated by aerosol inoculation covered the spectrum of symptoms seen in natural infections, the disease observed in study participants infected experimentally by intranasal drops was milder, with a longer incubation time and usually no involvement of the lower respiratory tract. For safety reasons, this finding led to the adoption of intranasal drop inoculation as the standard procedure in human experimental infections with influenza virus. 
 
These experiments and observations strongly support the view that many, possibly most, natural influenza infections occur by the aerosol route and that the lower respiratory tract may be the preferred site of initiation of the infection.
 
Epidemiologic Observations
In natural infections, the postulated modes of transmission have included aerosols, large droplets, and direct contact with secretions because the virus can remain infectious on nonporous dry surfaces for <48 hours. Because in practice completely ruling out contributions of a given mode of transmission is often difficult, the relative contribution of each mode is usually difficult to establish by epidemiologic studies alone. However, a certain number of observations are consistent with and strongly suggestive of an important role for aerosol transmission in natural infections, for example the "explosive nature and simultaneous onset [of disease] in many persons", including in nosocomial outbreaks. The often-cited outbreak described by Moser et al. on an airplane with a defective ventilation system is best accounted for by aerosol transmission. Even more compelling were the observations made at the Livermore Veterans Administration Hospital during the 1957-58 pandemic. The study group consisted of 209 tuberculosis patients confined during their hospitalization to a building with ceiling-mounted UV lights; 396 tuberculosis patients hospitalized in other buildings that lacked these lights constituted the control group. Although the study group participants remained confined to the building, they were attended to by the same personnel as the control group, and there were no restrictions on visits from the community. Thus, it was unavoidable at some point that attending personnel and visitors would introduce influenza virus in both groups. During the second wave of the pandemic, the control group and the personnel sustained a robust outbreak of respiratory illness, shown retrospectively by serology to be due to the pandemic strain influenza A (H2N2), whereas the group in the irradiated building remained symptom free. 
 
Whereas UV irradiation is highly effective in inactivating viruses in small-particle aerosols, it is ineffective for surface decontamination because of poor surface penetrations.  It is also ineffective for large droplets because the germicidal activity sharply decreases as the relative humidity increases. Furthermore, because the installation of UV lights was set up in such a way as to decontaminate the upper air of rooms only, large droplets would not have been exposed to UV, whereas aerosols, carried by thermal air mixing, would have been exposed. So in effect in this study only the aerosol route of infection was blocked, and this step alone achieved near complete protection.
 
Discussion and Implications for Infection Control during Influenza A (H5) Pandemic
Evidence supporting aerosol transmission, reviewed above, appears compelling.  Despite the evidence cited in support of aerosol transmission, many guidelines or review articles nevertheless routinely state that "large droplets transmission is thought to be the main mode of influenza transmission" (or similar statements) without providing supporting evidence from either previously published studies or empirical findings. Despite extensive searches, I have not found a study that proves the notion that large-droplets transmission is predominant and that aerosol transmission is negligible (or nonexistent).
Visit us at Greenbuild International

Dynamic Air Quality Solutions Booth # 5248
 
The USGBC Greenbuild International Conference and Expo is heading to the American Southwest.  This years show promises to be the largest ever.  Sheryl Crow and Al Gore will open the conference.  Visit Dynamic Air Quality Solutions on the upper level at the Phoenix Convention Center, November 10-12, 2009. For more information, visit  www.greenbuildexpo.org.
 
 
See Us at the World Energy Engineering Congress
 
Washington D.C. November 4-6, 2009 
 
The Association of Energy Engineers is again bringing the WORLD ENERGY ENGINEERING CONGRESS (WEEC) to Washington, DC for 2009. Now in its 32nd year, the WEEC is well-recognized as the most important energy event of national scope for end users and energy professional in all areas of the energy field. It is billed as the one comprehensive forum where you can fully assess the "big picture" - and see exactly how economic and market forces, new technologies, regulatory developments and industry trends all merge to shape our energy and economic future.

 

The WEEC features a large, multi-track conference agenda, a full line-up of seminars on a variety of current topics and a comprehensive exposition where Dynamic Air Quality Solutions will be exhibiting along with other promising new technologies. For more information, visit www.energycongress.com.f you have a unique Dynamic Air Cleaner application or installation, we would love to hear about it. Please let us know by dropping a line to Rob Goodfellow at rgoodfellow@DynamicAQS.com.
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About Dynamic Air Quality Solutions
Since 1982, Dynamic Air Quality Solutions' mission to its customers has been to develop and bring to market innovative, technologically advanced and affordable solutions to help clients optimize air quality, energy consumption, and the environment. For more information, visit our website at www.DynamicAQS.com/commercial/.