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  • Masks & Flu Transmission

    (Interesting how they are beginning to admit that no one ever established how flu is transmitted!)

    Review finds little evidence of airborne spread of flu
    Maryn McKenna Contributing Writer

    Editor's note: This story was revised Mar 14 to correct a misquote that was attributed to Michael T. Osterholm and to include qualifying details that were omitted from the earlier version.

    Mar 13, 2007 (CIDRAP News) ? A rigorous review of research into influenza transmission concludes that the virus is primarily transmitted at close quarters, a finding that downplays the likelihood of airborne transmission, particularly in healthcare settings, and could have implications for pandemic planning.

    In the April 1 issue of Lancet Infectious Diseases, published online ahead of print, Gabrielle Brankston and colleagues of Toronto's University Health Network describe their evaluation of 32 experimental and observational studies that they sifted out of 2,012 citations addressing flu transmission in the English-language literature.

    They come to two conclusions. First, that despite more than 70 years' research, much of what is believed to be known about flu transmission is based on poorly structured studies or faulty interpretations of results.

    And second, that the preponderance of the robust evidence supports flu being acquired only within a short distance of an infected person?making it much more likely that the virus is transmitted by large respiratory droplets that fall out of the air within several feet, rather than by fine aerosols that can travel long distances and hang in the air for extended periods of time.

    The authors found evidence that flu "may be transmitted by the airborne route under certain experimental conditions," the report says. Overall, however, the evidence suggests that airborne transmission, "as traditionally defined, is unlikely to be of significance in most clinical settings."

    "Our final conclusion was that we cannot say flu is transmitted over long distances, and the only way flu can transmit over long distances would be through the airborne route," Dr. Michael Gardam, an epidemiologist and the study's senior author, said in an interview. "It really seems to transmit via close contact, which is traditionally understood to be droplet or direct or indirect contact. We cannot rule out airborne transmission, but we see no evidence of airborne transmission?and so we think it is unlikely to be a major player in the overall epidemiology."

    The team's finding is the latest entry, though likely not the last, in a vigorous ongoing debate over flu transmission. The issue is vital for pandemic planning because assessment of transmission risk drives decisions about prevention?in particular, whether to offer health care workers surgical masks, which catch droplets, or respirators, which block airborne particles and may intercept flu viruses.

    The masks-versus-respirators issue is one of the most sensitive in pandemic planning. N-95 respirators are hard to wear correctly, especially for long periods of time, and respirator manufacturers have conceded that global demand in a pandemic would outstrip their production capacity. Acknowledging those difficulties, the US, Canadian, and British pandemic flu plans all initially recommended surgical masks for health care workers in almost all situations.

    But in Canada?where the airborne disease SARS (severe acute respiratory syndrome) shut down the city of Toronto for several weeks in 2003?the Ontario Nurses Association has threatened work stoppages if its members do not receive N-95 respirators during a pandemic. And in the United States, the Centers for Disease Control and Prevention expanded its guidance on respirator use last October under pressure from the healthcare industry, and now says using a respirator is "prudent" for any healthcare worker in contact with a known or potentially infected patient.

    In September, an article in Emerging Infectious Diseases charged that health care workers would be inadequately protected by masks and should receive respirators. In December, a research report in the American Journal of Industrial Medicine suggested that masks protect nearly as well against aerosols as respirators do?a finding that was quickly challenged by others, including experts working for mask and respirator manufacturers (see link to previous story below). And in February, the Institute of Medicine held a daylong workshop on pandemic protection for healthcare workers, though it will not report its recommendations until September.

    Dr. Eric Toner, senior associate at the University of Pittsburgh Medical Center's Center for Biosecurity and author of several articles on flu protection during a pandemic, applauded the Toronto group's review of flu-transmission research for making explicit how little solid evidence exists.

    "A lot of our assumptions turn out to be based on urban legends, or extrapolations made from incomplete information," he said. ""It lays out that so much of what we thought we know, we really don't know."

    But because the review makes clear how much remains to be proved, Toner said, flu protection measures should remain conservative, especially for healthcare workers.

    "My thinking is, people who are going to have close contact with pandemic-flu patients should wear the greatest degree of protection available, which is in most circumstances an N-95 (respirator)," he said. "And since there is a limited supply of N-95s, they ought to be saved for those people at highest risk of exposure. In the absence of clear answers, we ought to err on the side of caution."

    Michael T. Osterholm, PhD, MPH, director of the University of Minnesota Center for Infectious Disease Research and Policy, publisher of CIDRAP News, expressed skepticism about the authors' conclusion that airborne transmission is unlikely to be a significant factor in spreading flu. He said that view doesn't fit well with the seasonal flu's typical pattern of erupting nearly simultaneously in widely separated places.

    "From my 30 years of experience I've always been impressed with how seasonal flu functions on a community basis in a way that suggests it could be an aerosol-transmitted disease," he said. "We can see outbreaks in areas that are separated by hundreds of miles; that's much more consistent with an aerosol-transmitted pathogen?though that doesn't prove aerosol transmission. Pandemics have marched around the world in weeks to months in eras before we had jet planes. That smacks much more of an agent that's transmitted by the aerosol route."

    Gardam, the senior author, said the team hopes the paper will stimulate two initiatives: greater attention to antiviral prophylaxis for pandemic flu, and fresh attempts to conduct robust flu research.

    "The question of respiratory-protection policy has gone far beyond science at this point," he said. "But I hope people will be willing to say that we have to do really well-done studies so that the results can inform future decisions."

    Brankston G, Gitterman L, Hirji Z, et al. Transmission of influenza A in human beings. Lancet Infect Dis 2007 Apr 1 (early online publication Feb 19)

  • #2
    Re: Osterholm Hates New Study Re Masks & Transmission

    Excellent post. Personally, I will be putting any flu pts I take care of on "airborne isolation" instead of "droplet isol" whether our ID dep't heads order it or not.

    Comment


    • #3
      Re: Masks & Flu Transmission

      I recently assisted in a study to determine how available materials compared to P-100 respirator cartridges. Cartridges were opened, the contents removed, and a series of different materials were attached to the cartridges. The cartridges were installed onto standard North full-face respirators. A Certified Industrial Hygenist performed fit testing on the mask assembly using a standard quantitative fit testing machine, the one that compares particle counts inside the mask to ambient air particulate counts.

      The materials tested were:
      coffee filters, 1 layer;
      t-shirt fabric (knitted fabric), folded into 8 layers, wet, dry, and oiled with petroleum jelly;
      bandanas(woven fabric), folded into 8 layers, wet, dry, and oiled with petroleum jelly;
      a HEPA vacuum cleaner filter, dry.

      We boiled the cloth to shrink it before testing.

      The performance of the coffee filter, HEPA filter, and the dry fabric was terrible. Abysmal. Worthless. Bad.

      The wet fabrics were a bit better, but still bad. Why firefighters use wet bandanas to filter smoke is beyond me. They are practically worthless.

      The HEPA filter was so moisture-resistant that the mask fogged up to where you couldn't see out. And it didn't perform that well. Perhaps its stiffness made the seal leak, it really should have done much better.

      But the 8-layer oiled bandana and oiled t-shirt performed about 80% as well as the P-100 filter, and in fact passed about half the tests. This makes it equivalent to about a N-90, which is 90% as good as a N-95 filter. It was nothing short of amazing how well the oiled fabric filtered air.

      Now it's interesting that there is a report from WW1 that a doctor on a troop ship made everyone wear oiled gauze masks, and did not lose a single person on the trip across the Atlantic.

      Using an old-style cloth surgical mask and oiling it with petroleum jelly increases its filtration efficiency something like 1000 times. And oiled cloth filters actually filter better the dirtier they get, until they clog up. They are used in high-perforance cars.

      Oh, and I suppose I ought to admit it was my kid's science fair project.

      Comment


      • #4
        Re: Masks & Flu Transmission

        what kind of Hepa-filter ? (EN 1822)
        did they test surgical masks,N95s,P100s,FFP2s,FFP3s too ?
        I'm interested in expert panflu damage estimates
        my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

        Comment


        • #5
          Re: Masks & Flu Transmission

          wetdirt, can you give us link to that info on the WW1 doctor story?
          That would be really good. Thanks.

          Comment


          • #6
            Re: Masks & Flu Transmission

            "airborn over long distances" as in birds, flies, planes? How long is long?
            Maybe once there are enough N95 masks for everyone, we will know just how the flu is transmitted?

            Comment


            • #7
              Re: Masks & Flu Transmission

              Originally posted by Blue View Post
              wetdirt, can you give us link to that info on the WW1 doctor story?
              That would be really good. Thanks.

              page 1
              http://memory.loc.gov/service/sgp/sg...9181101/01.pdf
              page 2
              http://memory.loc.gov/service/sgp/sg...9181101/02.pdf


              I looked up 'Albolene" and it's a mixture of petroleum jelly and baby oil, with a few other things. The active ingredient is petrolem jelly. It makes the cotton fibers sticky. And having personally tested this one, I can say it is not difficult to breathe through.

              Comment


              • #8
                Re: Masks & Flu Transmission

                Originally posted by gsgs View Post
                what kind of Hepa-filter ? (EN 1822)
                did they test surgical masks,N95s,P100s,FFP2s,FFP3s too ?
                We tested all the materials against the P-100s, so yes, we tested the P-100. We didn't have any of the others. The HEPA was an EN 1822, I think, it didn't have any markings. The point was not to test everything on the market. The point was to test common materials found around the house to find the best material for a mask.

                Comment


                • #9
                  Re: Masks & Flu Transmission

                  well, once the particles are smaller than 5micron, then it seems that
                  they flow in the air just like molecules.

                  When a droplet falls down to the ground after sneezing, what happens to it ?
                  It dries out and viruses in it can be blown into air by wind easily ?

                  Is there anything that holds the viruses in dried droplets to the ground ?
                  Do they glue together of glue to dust-particles by electrostatic forces ?


                  Then there is the question whether viruses in low quantity dissolved in large masses of air are capable of infecting people.
                  Maybe it's just that droplets full of viruses are usually required
                  to initiate infection.

                  Maybe airborne viruses are even advantageous, they don't cause
                  infection but trigger immune response ? Then the virus should
                  try to avoid it...
                  I'm interested in expert panflu damage estimates
                  my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

                  Comment


                  • #10
                    Re: Masks & Flu Transmission

                    Well, once the particles are smaller than 5micron, then it seems that
                    they flow in the air just like molecules.
                    When a droplet falls down to the ground after sneezing, what happens to it ?
                    ...
                    It dries out and viruses in it can be blown into air by wind easily ?
                    No, they are more like very fine dust. Also the virus dries out and dies more readily. Also the number of viruses per cubic meter rapidly decreases by mixing, so the number of viruses inhaled decreases. I think there is a decreasing probability of infection with decreasing number of virions, but I don't remember if it is linear or asympotic. Maybe someone else might remember?



                    And there is some evidence that *eating* the virus promotes immunity better than *breathing* it, at least in cats, rats, and dogs. Maybe in people, but I don't think any studies have been done. It has to do with different receptors in the gut than in the lung.

                    Comment


                    • #11
                      Re: Masks & Flu Transmission

                      don't viruses survive better in dry environments, low humidity ?
                      They should survive many hours or days on floors or
                      other surfaces, I assume.

                      They really should test this, if they didn't already.
                      Just let flu-people sneeze on the floor and then let the mice in.
                      Or sneeze on the floor and then put a lattice over the floor
                      at -say- 1m height which doesn't stop the wind and let the
                      mice walk above the lattice.
                      Or sneeze on the floor and then keept watching the droplets
                      with electron microscope.
                      Or...
                      I'm interested in expert panflu damage estimates
                      my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

                      Comment


                      • #12
                        Re: Masks & Flu Transmission

                        But the 8-layer oiled bandana and oiled t-shirt performed about 80% as well as the P-100 filter, and in fact passed about half the tests. This makes it equivalent to about a N-90, which is 90% as good as a N-95 filter. It was nothing short of amazing how well the oiled fabric filtered air.
                        Very interesting wetDirt.

                        Can you tell me how you 'oiled' the t-shirt material.

                        How much did you put on, was it a measured amount?

                        Comment


                        • #13
                          Re: Masks & Flu Transmission

                          after what I read it's better than linear, so being exposed
                          twice to a single dose less likely results in infection
                          than being exposed once to a double dose
                          I'm interested in expert panflu damage estimates
                          my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

                          Comment


                          • #14
                            Re: Masks & Flu Transmission

                            have you put the oily masks under the microscope ?
                            I'd like to see how the fibers look like
                            I'm interested in expert panflu damage estimates
                            my current links: http://bit.ly/hFI7H ILI-charts: http://bit.ly/CcRgT

                            Comment


                            • #15
                              Re: Masks & Flu Transmission

                              No, **I** haven't, but the race-car people have, and so have Mercedez-Benz. There is a lot of information on oiled gauze air filters for the auto industry. (Oiled-gauze doesn't need to be changed for like 50,000 miles and even though initially more expensive, they can be cleaned, reoiled, and put back in the car 25 times.) They also discuss foam filters and paper filters. They are the ones who say that 8 layers is optimal for oiled gauze. They also have done tests where they run test engines and then saw them up and look for wear under the microscope, something I am reluctant to do on myself. Off-road motorcycle people have endless debates about them.

                              ----------------------------
                              I've also worked up a version of the 'simple mask' for the fashion concsious: Take 2 bandanas. (These are brightly colored 100% cotton handkerchief/scarfs measuring about 20"x20".) Fold one in half (2 layers), in half again (4 layers), and in half again (8 layers). This will be the filter portion and goes across your nose and mouth and wraps partly around the jaw. Smear this with petroleum jelly. For easier smearing, warm up the p.j. and add a few spoonfuls of baby oil. I didn't measure the amount, but smeared it visually. The oiled fabric goes a bit dark, so it's easy to tell if any spots are missed. I would guess that I used about a soup-spoon full.

                              Take the second bandana, the 'fashion bandana', and fold it diagonally into a triangle, bank-robber-style. Tie a knot in the point under the chin, and adjust the knot up or down to get a good fit cupping the chin. Roll long ways along the diagonal edge until about 4 inches are consumed. To close the gap on either side of the nose, take 2 cotton balls, unroll the edge a bit, stick a cotton ball into the spot where the gap would be, and roll back up. Try it for fit and move the cotton ball into the best spot to close the gap, and adjust the number of rolls to fit the face vertically.

                              Lay the oiled gauze filter parallel to the rolled diagonal edge and centered over the mouth and nose. A few stitches with a needle and thread will keep things from shifting, but the unhandy could probably use a stapler for the same thing, minding the pointy ends.

                              Tie the mask at the back of the head. If there are gaps along the cheekbones, an elastic headstrap going up and over the head might be necessary, but mine doesn't gap and actually fits very well. Your head may vary.

                              This mask has the advantage that it works fine with beards.

                              And it's washable, up to 25 times. Recoating is needed after every wash.

                              added note: Using mentholated petroleum jelly (like Vick's) would add another layer of mild antibiotic. Adding iodine, as in Betadine, would add more protection. There is an article in ProMed from Japan where they tested iodine-treated cloth and found it killed viruses. Just remember to renew it after washing.
                              Last edited by wetDirt; April 5, 2007, 11:07 AM.

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