Dödligt virus från Kina orsakar panik (SARS-CoV-2, COVID-19)

http://ldh.la.gov/assets/oph/Center-PHCH/Center-CH/infectious-epi/HAI/InfectionsbyAerosolsDropletsHandout.pdf

Based on size and persistence as an aerosol, the World Health Organization uses a particle diameter of 5 𝜇𝜇m to delineate between •Airborne (≤ 5 𝜇𝜇m) (5 Micromicrons
= 5.0E-6 Micrometers ) •Droplet (> 5 𝜇𝜇m) transmission

[Micromicrons] symbol/abbrevation: (μμm)


Bio-aerosol Size Bio-aerosols size and reach into the Respiratory Tract:•>10 μm in aerodynamic diameter blocked by nasal region •Between 5 and 10 μm deposit in the upper respiratory system •≤ 5 μm can reach the alveoli and cause lower respiratory tract infection

Droplet / AirborneDroplet transmission •Bio-aerosol likely to settle quickly, typically within 3 feet of source•Large particles > 5 μm•For droplet transmission: target (susceptible individual) must be close enough to source (infected individual) for the droplet (containing infectious microorganism) to make contact with the susceptible individual’s respiratory tract, eyes, mouth, nasal passagesAirborne transmission•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 Bio-aerosol Size and Persistence in the Air A droplet ofwill fall in100 μm10 seconds 40 μm1 minute 20 μm4 minutes 10 μm20 minutes5- 10 μm30-45 minutes≤ 5 μm Droplet nuclei May be inhaled to alveo

Electron micrographs of negative-stained 2019-nCoV particles were generally spherical with some pleomorphism (Figure 3). Diameter varied from about 60 to 140 nm. (0,06 - 0,14 micrometer.

Electron micrographs of negative-stained 2019-nCoV particles were generally spherical with some pleomorphism (Figure 3). Diameter varied from about 60 to 140 nm.

https://www.nejm.org/doi/full/10.1056/NEJMoa2001017

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4545937/

Particles of small size can remain suspended in the air for long periods, potentially exposing a large number of susceptible individuals, including those close to the source and those at greater distances [5]. A spherical particle of 4 μm in diameter takes 33 min to settle 1 m in still air, compared to a 1μm particle that will take 8 h [6]. Relative humidity, temperature and wind currents are the most important environmental factors that will determine the settling time of airborne particles that contain volatile components.

There is limited information in regards to the particle sizes with which infectious agents are associated. In humans, measures of particle size for influenza A virus (IAV) have been evaluated in controlled laboratory and health care settings, airplanes, daycares and households [6–10]. Distribution of IAV particle size varied between studies and settings, with IAV found in particles 1–4 μm in diameter (49% of particles) and particles > 4 μm (46% of particles) in health care facilities [7], and particles < 2.5 μm (64% of viral copies) detected in public places (i.e. health care, airplanes and day cares) [8]. Furthermore, dispersion models that have incorporated particle size information have indicated the plausibility of airborne transmission within these settings [3].

https://www.pnas.org/content/115/10/E2386

Influenza can potentially be transmitted from person to person by three modes:

Contact transmission, in which infectious secretions are transferred directly or indirectly via fomites;



droplet transmission, in which respiratory fluid-containing particles larger than 5 µm travel ballistically through the air and deposit onto mucous membranes within 3 ft as a result of gravity;

and airborne transmission, in which dried particles (i.e., droplet nuclei) smaller than 5 µm remain suspended in air and disperse over long distances and are inhaled and deposited in the respiratory tract.



Although influenza is thought to be transmitted via these non-mutually exclusive modes, the relative importance of each is unclear. It is especially challenging to delineate the relative significance of droplets vs. fine droplet nuclei in mediating influenza transmission in epidemiological studies, as the exposure history often cannot be clearly determined (4⇓–6). Precautions against droplet transmission include face masks and eye protection during close contact with a patient, whereas airborne precautions include single-patient negative pressure rooms and respiratory protection such as the use of an N95 respirator (7). Recommendation on influenza infection control measures in health care and community settings are formulated despite major knowledge gaps in the relative significance of the different transmission modes.

How Does Aerosol Transmission Occur?

A second area of controversy is whether pathogens can be aerosolized and transmitted by inhalation. NIOSH defines aerosols as a suspension of tiny particles or droplets in the air.[22] Aerosol transmission has been defined as person-to-person transmission of pathogens through the air by means of inhalation of infectious particles. Particles up to 100 μm in size are considered inhalable (inspirable). These aerosolized particles are small enough to be inhaled into the oronasopharynx, with the smaller, respirable size ranges (eg, < 10 μm) penetrating deeper into the trachea and lung (Figure).[23,24] Aerosols are emitted not only by "aerosol-generating procedures,"[19] but may also be transmitted whenever an infected person coughs, sneezes, talks, or exhales. Pathogens transmitted by respiratory aerosols can travel short or long range from the source depending on the size and shape of the particles, the initial velocity (eg, cough vs exhalation), and environmental conditions (eg, humidity, airflow).[25,26,27]

https://www.medscape.com/viewarticle/741245_3

https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/jam.14278

The dimensions of aerosolized virus particles vary widely, ranging from nanometre (e.g. ‘naked’ virus particles) to micrometre (e.g. viruses associated with nonviable particles) (Gerone et al. 1966). Once airborne, small particles containing virus(es) can remain airborne for long periods of time, allowing for their transport to other locations (Fig. 1). They also remain adrift in air (i.e. airborne) for longer periods of time primarily because of their low settling velocity, for example, from 3·1 × 10−3 m s−1 for 10‐μm particles to 3·5 × 10−5 m s−1 for 1 μm particles (Hinds 1998). Among nose breathers, larger particles (>5 μm) tend to deposit on the surfaces of the upper respiratory tract, whereas inhalation of small particles into the lower lungs may pose a greater risk for pneumonia/severe infection than what occurs with deposition onto the upper respiratory tract (Vincent 2005; Killingley and Nguyen‐Van‐Tam 2013). Overall, smaller particles that contain respiratory viruses are potentially more dangerous because they stay airborne longer (and thus the risk for acquiring an infection is prolonged), and they get inhaled into the lower lungs, potentially causing diseases with more severe outcomes.