Droplet infection

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Secretions from the respiratory tract in the form of droplets and aerosols reach the environment not only when sneezing unprotected

A droplet infection is an infection in which secretion containing pathogens from the respiratory tract gets onto the mucous membranes of other living beings. This happens through direct contact with the secretion droplets as droplet transfer or via the air as airborne transfer .

transmission

Breath flow when sneezing and the effect of barriers made visible with the help of streak photography

Saliva and other liquid secretions from the respiratory tract such as nasal secretions and sputum generally contain microorganisms , including pathogens . When exhaling, speaking, vomiting, sneezing and coughing, they are released into the environment as droplets and aerosols (droplet cores) through nebulization . Contact persons become infected when the pathogens then reach their mucous membranes - usually the upper respiratory tract, but it is also possible the conjunctiva of the eyes - and multiply there, which may trigger an infectious disease . The droplets containing the pathogen can also be spread via the hands or objects as a smear infection , for example when touching the mouth or eyes with unwashed or non-disinfected hands. The pathogens are surrounded by water as droplets. Once the water has evaporated, only a few pathogens survive for a long time.

Transmission by speaking

In airborne transmission, coughs and sneezes play a major role as dramatic expiratory events, releasing both easily visible droplets and large amounts of particles too small to be visible to the eye. But even with normal speech, large quantities of particles are produced that are too small to be seen, but large enough to transmit a large number of transmissible airway pathogens. Firstly, the rate of particle emission during normal speech is correlated with volume. It is sufficient for low to high amplitudes of around 1 to 50 particles per second. Second, when speaking, a small proportion of people behave in such a way that they consistently release an order of magnitude more particles than their peers. According to the research results so far, the phenomenon of speech superemission cannot be fully explained either by volume or by individual phonic structures. Other physiological factors, which vary widely from person to person, are thought to influence the likelihood of respiratory infection. These could also help explain the existence of super-spreaders , which are disproportionately responsible for airborne disease outbreaks. In the Heinsberg study is of Superspreading events at carnival events reported with loud talking and singing have strengthened the release of droplets and aerosols.

Classification

Particles in a bioaerosol usually have aerodynamic diameters in the size range from 0.01 µm to 100 µm.

droplet

Droplets on protective goggles after discussion with a person without a mouth and nose covering

Large droplets are more than 5  µm in diameter . After they have been exhaled, they sink rapidly and are only transmitted up to a distance of a meter or more. Droplets with a diameter of 100 µm need six seconds to sink to the ground from a height of two meters, droplets with a diameter of 10 µm 10 minutes. The maximum distance for an infection by small droplets has so far been given as only 1.5 meters. However, in a biophysical study by the Massachusetts Institute of Technology (MIT), which was carried out as part of the COVID-19 pandemic , it was found experimentally that fluid particles can be spread widely up to eight meters without a mechanical barrier when coughing or sneezing. These results challenge the droplet infection paradigm that dates back to the early twentieth century .

Droplet nuclei (aerosols)

Sizes of particles in aerosols.png

The dispersion of the finest liquid and / or solid particles ( microparticles ) in a gas with a diameter of less than 5  µm is called an aerosol . In the case of airborne transmission, the water cover of the droplets containing pathogens increasingly evaporates, so that they become lighter and lighter and can therefore float longer and longer in the air until only so-called droplet nuclei remain . These can be inhaled by other living beings in the immediate vicinity, whereby they get into the deeper airways due to their small size or are absorbed through the mucous membrane of the eyes. From a height of 2 meters, droplets with a diameter of 10 μm sink to the ground within 10 minutes if the air is still, and in the case of droplet cores with a diameter of 1 μm it takes 16.6 hours. With strong air movement, they can be transmitted up to 50 meters.

In one study, aerosols (<5 μm) containing SARS-CoV-1 or SARS-CoV-2 were generated using a nebulizer and fed into a Goldberg barrel to create an aerosolized environment. The inoculum gave cycle thresholds between 20 and 22, similar to those observed with samples from the upper and lower respiratory tract of humans. SARS-CoV-2 remained viable for 3 hours in aerosols, with a decrease in the infection titre measured similar to SARS-CoV-1. The mean half-lives of both viruses in aerosols were 1.1 to 1.2 hours. The results suggest that aerosol transmission of both viruses is plausible, as they can remain viable and infectious for hours in suspended aerosols. A previous study showed that the virus-containing aerosols float in the air for up to 3 hours. Virus-containing aerosols can be released as bioaerosols when speaking and singing, but also when breathing out, floating in the air for a long time and spreading in the room. A 2020 publication describes how aerosols containing viruses infected guests in a restaurant who were sitting in the air flow of an air conditioning system .

Diseases

Diseases that are mainly transmitted by droplets or droplet nuclei are primarily acute respiratory diseases (ARE) such as the so-called "cold", flu , COVID-19 , tuberculosis and streptococcal angina ; but measles and chickenpox also spread this way.

Classification

Infectious diseases that are transmitted by droplets with a size of 5 to 10 µm ( droplet infections ):

Transmission through droplet nuclei:

  • caused by bacteria: tuberculosis
  • viral causes: herpes zoster , measles, chickenpox

Protective measures

The pandemic triggered by the SARS-CoV-2 coronavirus has created an increased need for masks, as the population is also asked to wear masks ( everyday masks ).

The likelihood of a droplet infection can be reduced by spatial distancing . A full-face protection and protective glasses reduce the risk of infection, while the distance between the affected people the result. Internal and external protection can be increased by wearing a respirator without a valve, also combined with protective goggles or a face shield. The hygiene rules include compliance with the cough etiquette .

Example of influenza transmission

In the transmission of influenza viruses , this transmission path , in addition to the possible contact infection , plays the decisive role. The viruses can be excreted one day before the onset of the first symptoms of the disease up to an average of 7 days later - for children and immunosuppressed people possibly up to 21 days - and transmitted directly by droplet infection, these droplets, some of which are macroscopically visible, have a diameter of ≥ 5 μm.

Mouth and nose protection

According to the “Influenza Pandemic Plan Schweiz” published by the Federal Office of Public Health , November 2007 version, no studies had been published in relation to the protective effect of wearing mouth and nose protection in the general population against droplet infection by influenza viruses. “However, from experience with SARS , there were indications that the transmission of viruses can be restricted by hygienic masks.” A study from 2020 found that mouth and nose protection significantly reduced the release of influenza viruses and seasonal coronaviruses, especially if not only the staff, but above all the infected person, is equipped with it and that the transmission can be reduced with it.

Web link

Individual evidence

  1. ↑ Ines Kappstein: Nosocomial Infections: Prevention - Laboratory Diagnostics - Antimicrobial Therapy. Thieme, 2009, ISBN 978-3131484741 , p. 47.
  2. ↑ Entry ports for pathogens. Infektionsschutz.de; accessed on March 17, 2020
  3. ^ Christian Jassoy, Andreas Schwarzkopf: Hygiene, Infectiology, Microbiology. Thieme, Stuttgart 2018, p. 32, ISBN 978-3-13-241368-9 .
  4. ↑ Santiago Barreda, Nicole M. Bouvier, William D. Ristenpart et al .: Aerosol emission and superemission during human speech increase with voice loudness Scientific Reports volume 9, Article number: 2348 (2019)
  5. ↑ Hendrik Streeck1, Bianca Schulte et al .: Infection fatality rate of SARS-CoV-2 infection in a German community with a super-spreading event, page 12
  6. ↑ NTV: Ventilation is more important than wiping
  7. ↑ NTV: Transmission of the coronavirus - speaking is possibly the greatest danger
  8. ↑ Wolfgang Mücke, Christa Lemmen: Bioaerosols and health. Effects of biological air constituents and practical consequences ecomed medicine, 2008.
  9. ^ Andreas F. Widmer, Andreas Tietz: Practical Hygiene in the Doctor's Practice . In: Swiss Medical Forum . No. 5 , 2005, p. 660-666 , doi : 10.4414 / smf.2005.05581 .
  10. ↑ a b Notes on particle sizes in infectious aerosols. TRBA 250 Biological agents in health care and welfare, as of May 2, 2018, p. 80; accessed on May 15, 2020
  11. ^ A b Christian Jassoy, Andreas Schwarzkopf: Hygiene, Infectiology, Microbiology. Thieme, Stuttgart 2018, p. 34.
  12. ↑ Lydia Bourouiba: Turbulent Gas Clouds and Respiratory Pathogen Emissions. Potential Implications for Reducing Transmission of COVID-19 . In: JAMA . March 26, 2020, doi : 10.1001 / jama.2020.4756 (English).
  13. ↑ a b c Markus Dettenkofer, Uwe Frank, Heinz-Michael Just, Sebastian Lemmen, Martin Scherrer: Practical hospital hygiene and environmental protection. 4th edition, Springer-Verlag, Berlin 2018, p. 114
  14. ^ A b c Christian Jassoy, Andreas Schwarzkopf: Hygiene, Infectiology, Microbiology. Thieme, Stuttgart 2018, p. 33.
  15. ↑ Neeltjevan Doremalen, Dylan H.Morris, Myndi G.Holbrook et al .: Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1 The New England Journal of Medicine, May 2020th
  16. ↑ Joshua L. Santarpia1, Danielle N. Rivera et al .: Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Cente
  17. ↑ NDR: Now common sense is required Interview with Christian Drosten
  18. ↑ NTV: Transmission through aerosols comes into focus
  19. ↑ Infectious coronaviruses discovered in aerosols
  20. ↑ Jianyun Lu, Jieni Gu, Kuibiao Li et al .: COVID-19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020 Centers for Disease Control and Prevention 2020
  21. ↑ Federal Center for Health Education: How is the novel coronavirus transmitted? Infektionsschutz.de, as of March 12, 2020, p. 1; accessed on March 13, 2020.
  22. ↑ Anna Davies et al .: Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?
  23. ↑ a b Influenza Pandemic Plan Switzerland, November 2007 version, page 104 (a) or page 113 (b ( Memento from May 9, 2009 in the Internet Archive )) (PDF) Federal Office of Public Health, www.bag.admin.ch
  24. ^ Nancy HL Leung, Daniel KW Chu et al: Respiratory virus shedding in exhaled breath and efficacy of face masks
  25. ↑ Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering