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Ursprungligen postat av
ankademiker
Teknisk innebär väl luftburet att de kan flyga långa sträckor med vindar, lite som pollen? Aerosoler med viruset finns dock upp till 30 min i luften efter att smittad hostat. En studie sa upp till (vill jag minnas) 3 timmar i utrymme utan ventilation. Sorry att jag saknar länkar. Smart handla när affärer öppnar...
Vetenskapen drar inte en exakt storleksmässig/distributionsmässig gräns för smitta genom partiklar via utandningsgenererad aerosol.
WHO har en egen definition, vilken ifrågasätts av världens ledande forskare.
Enligt studier distribueras Corona genom utandning i olika hastigheter och då rikligt som aerosol 0-100 µm. Över 100 um sjunker snabbt mot marken. Medans de andra dropparna faller långsammare beroende på storlek/luftfuktighet/temperatur/vindströmmar etc.
Dessa distribuerade aerosoler tas upp av de övre luftvägarna samt lägger sig på ögonens slemhinna på exponerade människor i närheten.
FHM har lagt fokus på
ytorna dessa (större) droppar lägger sig på. De har bestämt sig för att gå på WHO´s definition, bias = kontaktsmitta.
Samtidigt har FHM sedan början av utbrottet fokuserat på just aerodynamiskt driven aerosol, dock uteslutande genom genom hosta, FHM nämner inte halveringstiden samt skillnaden på dropparna vilka färdas ut ur luftvägarna genom hostan. FHM nämner inte vanlig utandning vid tal/sång/andning, vilken innehåller aerosoler vilka blandas i närluften 1-2 meter.
Studier bekräftar halveringstiden på 35-40 minuter på droplets i storleken 5-10 μm.
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Infections by Bio-aerosols
http://ldh.la.gov/assets/oph/Center-...etsHandout.pdf
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Bio-aerosol Size Bio-aerosols size and reach into the Respiratory Tract:•
>10 μm in aerodynamic diameter
blocked by nasal region.
"Blocked" betyder alltså att Corona samlas i näsan.
Between 5 and 10 μm deposit in the upper respiratory system.
5-10 μm = övre luftvägar.
Trots denna studie väljer WHO att sätta gränsen för luftburen = <5 μm.
≤ 5 μm can reach the alveoli and cause lower respiratory tract infectionBased on size and persistence as an aerosol,
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the World Health Organization uses a particle diameter of 5 𝜇m to delineate between •Airborne (≤ 5 𝜇m) •Droplet (> 5 𝜇m) transmission
Edit : Här konstateras alltså droppar vilka mäter över 5 micrometer som ej luftburna av WHO, trots att de bevisligen tas upp av de övre luftvägarna.
Bio-aerosol remain suspended in air for long periods of time. Transported by air currents.
Small particles ≤ 5 μm :
# Target may be far away/different rooms.
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Bio-aerosol Size and Persistence in the Air :
A droplet of :
100 μm : 10 seconds
40 μm : 1 minute
20 μm : 4 minutes
10 μm : 20 minutes [Upper respiratory]
5-10 μm : 30-45 minutes. [Upper respiratory]
5 μm Droplet nuclei May be inhaled to alveoli [Deeper into lungs]
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Respiratory droplet characteristics are key to determine the droplet-borne pathogen transmission, which provide scientific basis for formulating the disease prevention from droplet transmission and control measures. Through studying the data information from existing documents, this paper gives the respiratory droplet characteristics, like size, concentration, velocity, etc. Meanwhile, droplet evaporation, droplet-borne pathogen activity and their transmission are discussed. The droplet size is no significant difference with human health level, gender and age. The size of droplets produced by health people is between 0.1 and 10 μm, it produced by patients is between 0.05 and 10 μm, and the patients’ droplet concentration is higher. The coughed droplet concentrations change with the size into a peak rule. The velocity of the cough droplets is the biggest, the range of 10 to 25m/s, the transmission distance is more than 2m.
https://www.sciencedirect.com/science/article/pii/S1877705815028519
Visst Droplet nuclei är mindre samt torkar ut snabbare väger mindre/färdas längre/har längre halveringstid samt färdas avsevärt längre sträckor då dessa dropp partiklar mäter <5 µm. De går djupare ner i luftvägarna, ända ner i alveoli.
Samtidigt har aerosoler vilka mäter 5-10 µm distribution samt halveringstid nog att sprida corona på tåg/busar/lokaler med mycket folk i.
Detta vet myndigheter WHO osv. Större partiklar = mer begränsade samhällsfunktioner.
Aerosoler dvs droppar i gasform "flyter/färdas/finns/" i luft beroende på dropparnas distribution/storlek samt rummets luftfuktighet/konditionering/vindströmmar/temperatur.
"respitary droplets" dvs aerosol genererad av vanlig utandning består av såväl "droplets" [droppar] med storlek
>5-20 µm [mikrometer], samt "Droplet nuclei" [mindre droppar]
<5 µm.
Detta handlar om aerosoler människor emellan!
Pratandes, andandes på +-2 meter´s avstånd.
Högst aktuellt med tanke på tunnelbana/bussar/restauranger/barer osv.
Forskare har med hjälp av elektron mikroskop, mätt Coronas sfäriskt formade partiklar - Virionerna [Viruspartikel].
Diameterna på dessa visade sig då variera, de minsta partiklarna mätte 0.06 microner (60 nanometer), de största på 0,14 microner (140 nanometer).
Ett hårstrå mäter ungefär 100 microner i diameter.
Ref.
A Novel Coronavirus from Patients with Pneumonia in China, 2019
https://www.nejm.org/doi/full/10.1056/NEJMoa2001017
WHO har en definition vilken unikt skiljer sig från vetenskapens.
Vetenskapen/forskare inom mikrobiologi har en annan.
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the study did find the presence of the virus in aerosol form. That there would be non-negligible amounts of virus in the air does not surprise Linsey Marr, a researcher at Virginia Tech
https://www.air.cee.vt.edu/about-linsey-marr.html
who studies the dynamics of viruses in the air.
“This is exactly what I suspected,” she says. Even before that paper came out, she’d told me it’s “
unfortunate” that the WHO insists on saying that the new coronavirus “is not airborne.”
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it’s “unfortunate” that the WHO insists on saying that the new coronavirus “is not airborne.”
http://ldh.la.gov/assets/oph/Center-...etsHandout.pdf
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Toward Understanding the Risk of Secondary Airborne Infection: Emission of Respirable Pathogens
Mark Nicas , William W. Nazaroff & Alan Hubbard
https://www.tandfonline.com/doi/full...59620590918466
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Certain respiratory tract infections are transmitted through air. Coughing and sneezing by an infected person can emit pathogen-containing particles with diameters less than 10 μ m that can reach the alveolar region.
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Characterization of infectious aerosols in health care facilities: An aid to effective engineering controls and preventive strategies
Eugene C. Cole, DrPH
, Carl E. Cook, MS
Durham, North Carolina
https://www.ajicjournal.org/article/...20aerodynamics
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Inherent in the infection process initiated by the inhalation of infectious droplet nuclei is the area of deposition within the respiratory tract. Such deposition is influenced by hygroscopicity, which causes an increase in the size of inhaled aerosols through moisture take up as they move within the airways. Knight59 estimates that a 1.5 μm hygroscopic particle—a common size in coughs and sneezes—increases to 2.0 μm in diameter when passing through the nose and to 4.0 μm in the saturated air of the nasopharynx and the lung. He further theorizes that the effect of hygroscopicity and the resultant particle size change increase retention in the tertiary bronchioles and alveolar ducts, an effect that may be significant for viral aerosols, which are highly infectious for that part of the lung.
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https://www.nature.com/articles/s41598-019-38825-y
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Data from randomized controlled trials of hand hygiene and surgical face masks in households provided evidence that aerosol transmission accounts for half of all transmission events.
A recent study with outpatients who tested positive for influenza A virus demonstrated that 53% and 42% produced aerosol particles containing viable influenza A virus during coughing and exhalation.
A mathematical model of influenza transmission within a household has suggested that the aerosol transmission route may not only be important, but indeed dominant8. Another mathematical model suggests that aerosol transmission is the dominant mode of transmission in long-term epidemics, whereas larger droplets could play a dominant role for short-term epidemics with high attack rates5.
...lyssnar på pressträffen.
