Abstract:
Microbicidal air filter for use with an air passageway, which comprises an immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and kill microbes suspended in a volume of air moving through the air passageway. The immobilization network is substantially permeable to air. A microbicidal facemask and a microbicidal air filter used in an air circulation system using the immobilization network are disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part (C.I.P.) of application Ser. No. 09/982,804, filed on Oct. 22, 2001, now abandoned. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention concerns air filters, more particularly microbicidal air filters.  
         BACKGROUND OF THE INVENTION  
         [0003]    Removing airborne pathogens and environmental allergens is very important in environments that require high levels of air purity, such as in hospitals and in houses of people suffering from severe allergic responses to the aforesaid allergens. Typically, devices in the form of masks or in-air duct filters filter out particulate material during either air circulation or, in the case of facemasks, during inhalation and exhalation. The facemasks and air duct filters temporarily capture the pathogens and allergens, and particulate matter such as dust, on a surface of a filtering material. Once the filters reach a threshold limit or after a single use, they are typically discarded or in some cases, cleaned and reused. Many designs of filtering devices exist, examples of which are as follows:  
           [0004]    U.S. Pat. No. 1,319,763, issued Oct. 28, 1919, to Drew for “Air filter for wall registers”;  
           [0005]    U.S. Pat. No. 3,710,948, issued Jan. 16, 1973, to Sexton for “Self-sustaining pocket type filter”;  
           [0006]    U.S. Pat. No. 3,779,244, issued Dec. 18, 1973, to Weeks for “Disposable face respirator”;  
           [0007]    U.S. Pat. No. 3,802,429, issued Apr. 9, 1974, to Bird for “Surgical face mask”;  
           [0008]    U.S. Pat. No. 4,197,100, issued Apr. 8, 1980, to Hausheer for “Filtering member for filters”;  
           [0009]    U.S. Pat. No. 4,798,676, issued Jan. 17, 1989, to Matkovich for “Low pressure drop bacterial filter and method”;  
           [0010]    U.S. Pat. No. 5,525,136, issued Jun. 11, 1996, to Rosen for “Gasketed multi-media air cleaner”;  
           [0011]    U.S. Pat. No. 5,747,053 issued May 5, 1998, to Nashimoto for “Antiviral filter air cleaner impregnated with tea extract”; and  
           [0012]    U.S. Pat. No. 5,906,677, issued May 25, 1999, to Dudley for “Electrostatic supercharger screen”.  
           [0013]    The aforesaid designs suffer from a number of important drawbacks. Disadvantageously, in the above-mentioned designs removal of the dirty filter or the facemask after use may cause non-immobilized pathogens or particulates to be dispersed into the air immediately around the user, which, if inhaled may be hazardous to the user. In addition, the designs may not immobilize the air borne pathogens and kill them in situ. Some of the designs incorporate viscous material into the filter material to capture particulate material. Some designs incorporate complex arrangements of filters inside cartridges, which may be impractical for use in air ducts or in facemasks. In some cases, fiberglass is used as part of the filter medium, which may be harmful to humans if located near the nose and mouth. In one design, disinfectant soaked cotton wool appears to be located in an air duct for aerosolizing into a room to maintain moisture content. Use of such a wet disinfectant may be harmful to humans in close proximity to the disinfectant and may not be appropriate for use in a facemask.  
           [0014]    Further advantages of the invention will be in part obvious from an inspection of the accompanying drawings and a careful consideration of the following description.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention reduces the difficulties and disadvantages of the prior art by providing a microbicidal air filter, which captures and kills pathogenic microbes on a novel immobilization network of fibers. To achieve this, the fibers include an antimicrobial agent within their structure (impregnated therein), which substantially kills the microbes and retains them within the body of the fibers. This significantly reduces or essentially eliminates the problems associated with further release of the microbes from the filter after use and during disposal. Advantageously, the filter can be used as a facemask or in air-circulation ducts, typically as an after-filter or downstream of a filter, and can capture and kill a wide variety of microbes. Desirably, the fibers can be made of a material, which enables the filter to be washed and reused without significant loss of antimicrobial activity.  
           [0016]    Accordingly, in a first embodiment of the present invention, there is provided a microbicidal air filter for use with an air passageway, said air filter comprising: an immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and kill microbes suspended in a volume of air moving through said air passageway, said immobilization network being substantially permeable to said air.  
           [0017]    Accordingly, in a second embodiment of the present invention, there is provided a microbicidal air filter for use with an air passageway, said air filter comprising: an immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and substantially inhibit the growth of microbes suspended in a volume of air moving through said air passageway, said immobilization network being substantially permeable to said air.  
           [0018]    Accordingly, in a third embodiment of the present invention, there is provided a microbicidal face mask comprising: first and second air permeable screen elements secured together along respective peripheral edges, said screen elements defining a gap therebetween, said screen elements being configured and sized to fit over the mouth and nose of a user and to be secured thereto; an air permeable immobilization network located in and substantially filling said gap, said immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and kill microbes suspended in a volume of air moving through said network.  
           [0019]    Accordingly, in a fourth embodiment of the present invention, there is provided a microbicidal face mask comprising: first and second air permeable screen elements secured together along respective peripheral edges, said screen elements defining a gap therebetween, said screen elements being configured and sized to fit over the mouth and nose of a user and to be secured thereto; an air permeable immobilization network located in and substantially filling said gap, said immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and substantially inhibit the growth of microbes suspended in a volume of air moving through said network.  
           [0020]    Accordingly, in a fifth embodiment of the present invention, there is provided a microbicidal air duct filter for use in an air circulation system, said air duct filter comprising: first and second air permeable screen elements securable together along respective peripheral edges, said screen elements being configured and sized to fit in an air duct and to be secured therein; an air permeable immobilization network located substantially between said first and second screen elements, said immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and kill microbes suspended in a volume of air moving through said network.  
           [0021]    Accordingly, in a sixth embodiment there is provided a microbicidal air duct filter for use in an air circulation system, said air duct filter comprising: first and second air permeable screen elements securable together along respective peripheral edges, said screen elements being configured and sized to fit in an air duct and to be secured therein; an air permeable immobilization network located substantially between said first and second screen elements, said immobilization network having substantially impregnated therein an amount of at least one antimicrobial substance sufficient to substantially immobilize, retain and substantially inhibit the growth of microbes suspended in a volume of air moving through said network. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    In the annexed drawings, like reference characters indicate like elements throughout.  
         [0023]    [0023]FIG. 1 is a simplified exploded view of an embodiment of a filter;  
         [0024]    [0024]FIG. 2 is a simplified partial cutaway view of a facemask with the filter;  
         [0025]    [0025]FIG. 2 a  is a simplified partial cutaway view of an alternative embodiment of a facemask;  
         [0026]    [0026]FIG. 3 is a simplified exploded view of an embodiment of a filter in a frame;  
         [0027]    [0027]FIG. 4 is a simplified exploded view of the filter with a primary filter;  
         [0028]    [0028]FIG. 5 is a simplified exploded view of an air circulation system with a filter;  
         [0029]    [0029]FIG. 6 is simplified front view of an alternative filter for use in the system of FIG. 5;  
         [0030]    [0030]FIG. 7 is a simplified front view of an alternative filter for use with the system of FIG. 5, showing stitches as a fastening member;  
         [0031]    [0031]FIG. 8 is a simplified front view of an alternative filter for use with the system of FIG. 5, showing rivets as a fastening member; and  
         [0032]    [0032]FIG. 9 is a cross sectional view taken along lines  9 - 9  of FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    With reference to the annexed drawings the preferred embodiments of the present invention will be herein described for indicative purposes and by no means as of limitation.  
       Definitions  
       [0034]    As used herein, the term “microbe” or “microbial” is intended to mean microorganisms including, but not limited to, bacteria, protozoa, viruses, molds and the like. Also included in this definition are dust mites.  
         [0035]    As used herein, the term “antimicrobial agent” is intended to mean a compound that inhibits, prevents, or destroys the growth or proliferation of microbes such as bacteria, protozoa, viruses, molds and the like. Examples of antimicrobial agents as used herein include anti-bacterial agents, anti-viral agents, anti-mold agents, anti-yeast agents and anti-dust mite agents, or any combination thereof.  
         [0036]    As used herein, the term “anti-bacterial agent” is intended to mean a compound that inhibits, prevents the growth of, or kills bacteria.  
         [0037]    As used herein, the term “anti-viral agent” is intended to mean a compound that inhibits, prevents the growth of, or kills viruses.  
         [0038]    As used herein, the term “anti-mold agent” is intended to mean a compound that inhibits, prevents the growth of, or kills molds.  
         [0039]    As used herein, the term “anti-yeast agent” is intended to mean a compound that inhibits, prevents the growth of, or kills yeasts.  
         [0040]    As used herein, the term “anti-dust mite agent” is intended to mean a compound that inhibits, prevents the growth of, or kills dust mites.  
         [0041]    As used herein, the term “microbicidal” is intended to refer to the inhibition, growth prevention or killing properties of any of the aforesaid “agents”, used either alone or in combination with each other.  
       Preferred Embodiments  
       [0042]    Referring now to FIG. 1, a first embodiment of a microbicidal air filter shown generally at  10 . Broadly speaking, the filter  10  includes an air permeable immobilization network  12 , an air permeable first screen  14  and an air permeable second screen  16 . The first screen  14  and the second screen  16  are merely acting to support the network  12  and to define a work area  18 . One skilled in the art will recognize that the immobilization network  12  may be used independently of the screens  14  and  16 .  
         [0043]    The network  12  includes a mesh of fibers  20 , which can be non-woven or woven depending on whether a soft or hard (rigid) network is desired. The network  12  may also include yarn such as cotton in which the fibers  20  are interwoven. Each fiber  20  includes a quantity of at least one antimicrobial agent that is fully impregnated and integral with the body of the fiber  20  thereby providing a large concentration of the antimicrobial agent over a large surface area. The fibers  20  are arranged such that they are permeable to air over the entire mesh, typically as a fine layer of so-called angels hair, of flaky mesh or the like.  
         [0044]    Preferably, the network is a fibrous material. More preferably, the fibrous material is commercially available RHOVYL&#39;A.S.+™, RHOVYL&#39;As™, THERMOVYL-ZCB™, THERMOVYL-MXB™ or TRICLOSAN™ treated PVC organic fiber.  
         [0045]    Both RHOVYL&#39;A.S.+™, RHOVYL&#39;As™, THERMOVYL-MXB™ and THERMOVYL-ZCB™ are fibrous material that have instrinsic antimicrobial activity. In particular, the RHOVYL&#39;As™ fiber and the THERMOVYL-ZCB™ fiber contain an antibacterial agent, which is integrated, or impregnated therein, in the body of the fiber, whereas the RHOVYL&#39;A.S.+™ fiber antibacterial agent, the RHOVYL&#39;A.S.+™ fiber and the THERMOVYL-MXB™ fiber also contain acaricide, an anti-dust mite agent. TRICLOSAN™ is an antimicrobial agent, which reduces the growth or kills microbes such as bacteria, yeast and molds.  
         [0046]    The fibrous material is either used pure (100%) or in blends, with a percentage of at least 30% volume, along with other types of fibers within woven or non-woven type fabrics, and which meet the requirements of an individual protective equipment (IPE). The fibrous material may also have other properties including, but not limited to, non-flammability, resistance to chemical products, ignition suppression, thermal insulation, and moisture management.  
         [0047]    Preferably, the antimicrobial agents include an antibacterial agent, an anti-viral agent, an anti-dust mite agent, an anti-mold agent and an anti-yeast agent.  
         [0048]    Preferably, the anti-bacterial agent is TRICLOSAN™.  
         [0049]    Preferably, the anti-dust mite agent is benzyl benzoate.  
         [0050]    Typically, the fibrous material has porosity in the range of about 0.1 μm to about 3 μm, although this depends upon the size of microbe to be retained.  
         [0051]    Typically, the fibrous material has a density of between two grams per square foot (2 gr/ft 2 ) to thirty grams per square foot (30 gr/ft 2 ). More preferably, the density is around ten grams per square foot (10 gr/ft 2 ).  
         [0052]    As best illustrated in FIG. 2, the filter  10  may be part of a facemask  24  of the type normally used by hospital workers and the like and which could be expandable (soft mask) or not (rigid mask), that are sometimes used in areas with pre-filtered air. The screens  14  and  16  are typically connected around a peripheral edge  22  and define a gap  23  therebetween. The network  12  can be attached to one of the aforesaid screens to provide both a physical barrier against particulate material and more importantly, to pathogenic microbes. The network  12  can be attached to the screens  14  or  16  using a VELCRO™ type fastener, stitches, bonding and the like, or inside an individual portable mask  24  that are worn in front of the nose/mouth area of the individual. A front mask screen  25  of the mask  24  acts as a primary filter located upstream of the network  12  to pre-filter the air by removing particulate material and microbes from the air passing therethrough along an air passageway, as shown by the arrows.  
         [0053]    Alternatively, as best illustrated in FIG. 2 a,  the network  12  may be located between the front screen  25  and a rear screen  27 , such as commercially available filter masks, in the gap  23  of the facemask  24  to create a two-way system of filtration, as shown by the arrows. The front screen  25  may include a slit  29  to allow the network  12  to be inserted into the gap  23 . This type of facemask  24  may be useful for people who are suffering from a respiratory infection and who still wish to work yet, don&#39;t wish to infect others by exhaling breath contaminated with pathogenic microbes.  
         [0054]    The screen elements  14 ,  16  can have different sizes and shapes and can be simple typical flexible or semi-flexible type screens as illustrated in FIG. 1, made from aluminum, nylon, thermoplastic material, fiberglass type materials (usually not approved for mask applications), woven type fabrics or the like. As shown in FIG. 3, the screen elements  14 ,  16  and the network  12  can be supported by a rigid frame  26 , such as a standard aluminum screen frame, that is divided into two parts  28 ,  30  and integral with the screen elements  14 ,  16  respectively, to ensure rigidity and ease of installation. A fastening member  32  may be used to releasably connect the two screen elements  14 ,  16  together with the network  12  sandwiched therebetween and compressed to prevent it from being displaced by the air flowing therethrough. The fastening member  32  may be a pivoting retainer pivoting on one of the parts  28 ,  30  to retain the other part against the same. Alternatively, as best illustrated in FIG. 4, a rigid screen  34  of any existing air filter  36  may also be used.  
         [0055]    Referring now to FIGS. 5 and 6, the filter  10  is illustrated installed inside an air duct  38  downstream of the air filter  36  and upstream of an air heating system  40  (the arrows in FIG. 5 show the air passageway) such that the air passing through the network  12  is pre-filtered. The frame  26  generally encloses the screen elements  14 ,  16  but also includes intermediate reinforcing rods  42  used to subdivide the screen elements  14 ,  16  into a plurality of smaller sub-elements  44  to constrain the network  12  to remain in place between the two elements  14 ,  16 . Alternatively, as best seen in FIG. 6, the frame  26  is a thin metallic rod onto which the screens  14 ,  16  are attached, with reinforcing rods  42  providing additional support to the screen elements  14 ,  16  and to the network  12  and to provide the aforesaid sub-elements  44 .  
         [0056]    Referring now to FIGS. 5, 7,  8  and  9 , other types of fastening members  32  are illustrated. One preferable type of fastening member  32  includes a plurality of stitches  46  which may be arranged in a variety of patterns, for example wavy lines or straight lines. The stitches  46  pass through the network  12  and divide the network into subdivisions  44 , as previously described. Alternatively, as best illustrated in FIG. 8, the fastening members  32  may also include rivets  48 , which pass through the network  12 .  
       EXAMPLES  
       [0057]    The present invention is illustrated in further detail by the following non-limiting examples.  
       Example 1  
       [0058]    Evaluation of Microbicidal and Filtering Capacity of Rigid and Soft Facemasks  
         [0059]    As shown in Table 1, two facemasks of the present invention were compared to a commercially available facemask 1,2,3  for their antimicrobial and retaining capabilities against a panel of bacteria and molds of various sizes 4,5,6,7 . The NB rigid and soft masks used in Examples 1 and 2 were both equipped with a network  12  of PVC organic fiber containing TRICLOSAN™. The NB soft mask was composed of a double covering of woven type fabric containing 76% w/w THERMOVYL-ZCB™ fibers and 24% w/w polyester (although any other woven type fabric such as cotton or the like could have been used) stitched to each other at their periphery, within which the network  12  was located (see FIG. 2 a  above). The NB rigid mask was made of two conventional commercially available anti-dust masks, which were inserted one inside the other, between which the network of PVC organic fiber containing TRICLOSAN™ was located.  
         [0060]    An air contamination chamber 5,8,9  was used to measure the filtering capacity of a mask containing the network. The chamber includes a perforated bottle containing a predetermined quantity of lyophilized microorganisms. The chamber is installed on a microbiologic air-sampler. The test mask was installed at the interface between the contaminated air chamber and the air sampler. A negative pressure was generated in the air chamber, which caused the lyophilized microorganisms to move towards the mask. A culturing medium was located downstream of the mask to detect any breakthrough of the mask.  
                                                                         TABLE 1                                       Filtration efficiency (%)            Microorganisms   Size (μm)   NBRM   NBSM   3M*                    Bacteria              Mycobacteria     0.2-0.7 × 1.0-10   100   100   95         tuberculosis         Proteus spp.   0.4-0.8 × 1-3      100   100         Pseudomonas     0.5-1.0 × 1.5-5     100   100         aureginosa           Staphylococcus aureus     0.5 × 1.5   100   100         Streptococcus     0.5-1.5   100   100         pneumoniae           Haemophilius     1   100   100         influenze         Anthrax   1-1.5 × 3-5     100   100       Moulds         Acremonium strictum     3.3-5.5 (7) × 0.9 × 1.8   100   100   96         Aspergillus versicolor       2-3.5   100   100         Penicillium     2.5-3.5 × 2.2-2.5   100   100         griseofulvum           Neosartorya fischeri       2 × 2.5   100   100                                          
 
       Example 2  
       [0061]    Evaluation of Filtering of Small Particles  
         [0062]    The filtering capacity of the three masks of Example 1 was tested against two particulate materials of 0.3 μm particle size using essentially the same apparatus as in Example 1. A cartridge capturing membrane located downstream from an air pump, in this case, captured breakthrough particulates. The air pump creates a negative pressure downstream of the mask. The two particulate materials chosen were sodium chloride and dioctyl phthalate.  
                                             TABLE 2                                       Filtration efficiency (%)            Particulate material   Size (μm)   NBRM   NBSM   3M*               Sodium chloride (NaCl)   0.3   100   100   95       Dioctylphthalate (DOP)   0.3   100   100                                          
 
       Example 3  
       [0063]    Evaluation of Microbicidal and Filtering Capacity of a Ventilation System Filter  
         [0064]    The antimicrobial capacity of a filter of the embodiment of FIG. 3 with RHOVYL&#39;A.S.+™ fibers was evaluated after 0, 7, 14, and 21 days installation in a ventilation system in a house. The results are illustrated in Tables 3. to 6 below.  
         [0065]    The filters were removed after the aforesaid times and analysed using the Samson method 10 . The fibrous material (1 g) of each filter was diluted with demineralised, sterilized water (9 mL) and then serially diluted.  
         [0066]    The calculation of total amount of bacteria, yeast and molds were done using hemacytometry. The calculation of the total amount of viable bacteria, yeasts and molds were determined following a culture of the serial dilutions on appropriate media. The aerobic viable bacteria were cultured on soya agar-agar (TSA, Quelab), whereas the yeasts and molds were cultured on HEA supplemented with gentamycin (0.005% p/v) and oxytetracycline (0.01% p/v) to limit bacterial growth. HEA&#39;s pH of 4.8±0.2 allows the germination of spores and development of mycelens. After the incubation period, the calculation of microbial colonies was carried out using a colony meter (Accu-Lite™, Fisher). The morphotype of the bacterial colonies was identified by Gram staining (see Table 5).  
         [0067]    Concerning the yeasts and molds calculation, each macroscopically distinct mold colony was identified by gender and/or species using microscopy.  
         [0068]    Mold slides were prepared using the adhesive tape method 11 . This technique maintains the integrity of the mold structures by fixing them on the sticky side of the tape. Once collected, the molds were stained with lactophenol and observed at a magnification of 10× and 40×. Using identification keys 12,13,14,15 , the molds were identified. In this experiment only colonies that produced spores were identified.  
                                                                         TABLE 3                           Bacterial filtering                After filter   Calculated bacteria (UFC/g)                Time (days)   Viable   Non-viable   Total                            0    6000    169000    175000               (3.43%)   (96.57%)   (100%)           7    9000    318000    327000               (2.75%)   (97.25%)   (100%)           14   27000   1193000   1220000               (2.21%)   (97.79%)   (100%)           21   70000   3650000   3720000               (1.88%)   (98.12%)   (100%)                      
 
         [0069]    [0069]                                                                         TABLE 4                           Fungal filtering                After filter   Calculated fungi (UFC/g)                Time (days)   Viable   Non-viable   Total                            0    29000    218000    247000               (11.74%)   (88.26%)   (100%)           7    110000    970000    1080000               (10.19%)   (89.81%)   (100%)           14    230000    2400000    2630000                (8.75%)   (91.25%)   (100%)           21   1640000   21000000   22640000                (7.24%)   (92.76%)   (100%)                        
         [0070]    [0070]                                   TABLE 5                           Identification of bacterial morphotypes            After filter (days)   Bacterial morphotypes                    0   78.4% Cocci Gram positive           21.6% Rod Gram negative       7   84.3% Cocci Gram positive           15.7% Rod Gram negative       14   86.7% Cocci Gram positive           13.3% Rod Gram negative       21   88.9% Cocci Gram positive           11.1% Rod Gram negative                    
         [0071]    [0071]                                   TABLE 6                           Identification of mold species            After filter (days)   Mold species                    0     Aspergillus niger ,  Cladosporium               cladosporioides ,  Cladosporium herbarum,             Penicillium sp., yeasts       7     Aspergillus niger ,  Cladosporium               cladosporioides ,  Cladosporium herbarum,             Penicillium sp., yeasts       14     Alternaria alternata , Arthrinium sp.,             Aspergillus niger , Cladosporium sp.,           Geotrichum sp., Penicillium sp., yeasts       21     Aspergillus niger ,  Cladosporium               cladosporioides ,  Cladosporium herbarum,             Penicillium sp., yeasts                    
       Discussion  
       [0072]    To date, commercially available masks have been hampered by their inability to capture and kill in excess of 95% of microorganisms. A study of a microbicidal network of the present invention, in the form of the facemasks and filters in a ventilation system, has demonstrated a significant improvement in capturing and killing efficiency (Tables 1 to 6).  
         [0073]    Tables 1 and 2 illustrated the effectiveness of PVC organic fiber containing TRICLOSAN™ as particulate filters, anti-bacterial and anti-mold filters. For both the soft facemask and the rigid facemask, the anti-microbial and particulate filtering capacities were 100% compared to the corresponding capacities for a commercially available mask (95 to 96%).  
         [0074]    Tables 3 to 6 illustrate highly efficient levels of antimicrobial and filtering capacity of the filter of the present invention. Specifically, the inventor has demonstrated, in Tables 3 and 4, that the combined anti-bacterial, anti-fungal, and retaining capacities are each 100%.  
         [0075]    In addition, the inventor has demonstrated that different bacterial morphotypes, as is illustrated in Table 5, were captured on the filter after zero (0) days 96.6% (78.8% and 21.6% of cocci Gram-positive and rod Gram-negative type bacteria respectively) of the whole bacteria population present on the fibers of the filter. After twenty-one days (21) 98.1% (88.9% and 11.1% of cocci Gram-positive and rod Gram-negative type bacteria respectively) were present on the fibers of the filter. This demonstrates that the efficiency of the filer remains after an extended period. As illustrated in Table 6, a variety of pathogenic molds were identified on the filter of the present invention up to twenty-one days.  
         [0076]    If desired, the filter can be cleaned and reused without a significant loss of the aforesaid capacities (results not shown).  
         [0077]    A key feature of the filter  10 , whether it be in the aforesaid facemasks or the circulation system duct filter, is its ability to immobilize, retain and kill or inhibit the growth of a wide variety of microbes, which come into contact with the network  12  of fibers  20 . Air that is either pre-filtered, in the case of the circulation system, or inhaled/exhaled through the facemask by the user, often includes residual microbes that have either passed through the primary filter or the filter has failed to immobilize them. In the case where a person who uses the facemask of the present invention and who has an upper respiratory infection, such as influenza, tuberculosis, anthrax, severe acute respiratory syndrome (SARS) and the like, can significantly reduce or essentially eliminate further infection to other people. Similarly, air that is contaminated with pathogenic microbes can be filtered before entering into the nose and mouth area of the user. The flow of air is shown by the arrows in FIGS. 2, 2 a,  and  5 , in which air contaminated with microbes is shown as hatched lines and non-hatched arrows show clean, filtered air.  
       References (Incorporated Herein by Reference)  
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         [0079]    2. TB Respiratory Protection Program In Health Care Facilities Administrator&#39;s Guide, (http://www.cdc.gov/niosh/99-143.html).  
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         [0081]    4. MMWR; Laboratory Performance Evaluation of N95 Filtering Facepiece Respirators, 1996 (Dec. 11, 1998).  
         [0082]    5. Edwin H. Lennette, Albert Balows, William J. Hausler, Jr. H. Jean Shadomy, 1985, Manual of Clinical Microbiology.  
         [0083]    6. Robert A. Samson, Ellen S. van Reenen-Hoekstra, 1990, Introduction to food-borne Fungi.  
         [0084]    7. G. Nolt, Noel R. Krieg, Peter H. A. Sneath, James T. Staley, Stanley, T. Williams, 1994, Bergey&#39;s Manual of Determinative bacteriology.  
         [0085]    8. Fradkin A (1987) Sampling of microbiological contaminants in indoor air, In: sampling and calibration for atmospheric measurements ASTM Special Technical Publication, 957:66-77.  
         [0086]    9. 42 CFR Part 84 Respiratory Protective Devices, (http://www.cdc.gov/niosh/pt84abs2.html).  
         [0087]    10. Samson, R A. 1985.  Air sampling methods for biological contaminants.  Document de travail fourni au Groupe sur les champignons dans l&#39;air des maisons de Santé et Bien-être social Canada, Ottawa, Ontario, K1A 1L2.  
         [0088]    11. Koneman, W. E. et G. D. Roberts. 1985. Practical laboratory mycology 3rd ed. Williams and Wilkins. Baltimore, Md.  
         [0089]    12. Domsch, K. H., W. Gams et T.-H. Anderson. 1980. Compendium of soil fungi. Academic Press. London.  
         [0090]    13. Larone, D. H. 1987. Medically important fungi. A guide to identification. New York. Elsevier Science Publishing Co. Inc.  
         [0091]    14. Malloch, D. 1981. Moulds, their isolation, cultivation and identification. Toronto: University of Toronto Press. 97 p.  
         [0092]    15. St-Germain, G. et R. C. Summerbell. 1996. Champignons filamenteux d&#39;intérêt médical: Caractéristiques et identification. Star Publishing Company. Belmont, Calif.