Modes of transmission of the virus causing COVID-19



According to current evidence, COVID-19 virus is transmitted between people through respiratory droplets and contact routes.

Droplet transmission occurs when a person is in close contact (within 1 m) with someone who has respiratory symptoms (e.g. coughing or sneezing,) and is therefore at risk of having his/her mucosae (mouth and nose) or conjunctiva (eyes) exposed to potentially infective respiratory droplets (which are generally considered to be > 5-10 μm in diameter).
Droplet transmission may also occur through fomites in the immediate environment around the infected person.


Therefore, the transmission of the COVID-19 virus can occur by direct contact with infected people and indirect contact with surfaces in the immediate environment or with objects used on the infected person (e.g. stethoscope or thermometer)

Airborne transmission is different from droplet transmission as it refers to the presence of microbes within droplet nuclei, which are generally considered to be particles < 5μm in diameter, and which result from the evaporation of larger droplets or exist within dust particles. They may remain in the air for long periods of time and be transmitted to others over distances greater than 1 m.


In the context of COVID-19, airborne transmission may be possible in specific circumstances and settings in which procedures that generate aerosols are performed (i.e. endotracheal intubation, bronchoscopy, open suctioning, administration of nebulized treatment, manual ventilation before intubation, turning the patient to the prone position, disconnecting the patient from the ventilator, non-invasive positive-pressure ventilation, tracheostomy, and cardiopulmonary resuscitation). The analysis of 75,465 COVID-19 cases in China, the airborne transmission was not reported.
There is some evidence that COVID-19 infection may lead to intestinal infection and be present in feces. However, to date, only one study has cultured the COVID-19 virus from a single stool specimen. There have been no reports of fecal-oral transmission of the COVID-19 virus to date.

Conclusion

 Based on the available evidence, including the recent publications mentioned above, WHO continues to recommend droplet and contact precautions for those people caring for COVID-19 patients and contact and airborne precautions for circumstances and settings in which aerosol generating procedures are performed.
These recommendations are consistent with other national and international guidelines, including those developed by the European Society of Intensive Care Medicine and Society of Critical Care Medicine13 and those currently used in Australia, Canada, and The United Kingdom.  
At the same time, other countries and organizations, including the US Centers for Diseases Control and Prevention and the European Centre for Disease Prevention and Control, recommend airborne precautions for any situation involving the care of COVID-19 patients, and consider the use of medical masks as an acceptable option in case of shortages of respirators (N95, FFP2 or FFP3).
Current WHO recommendations emphasize the importance of rational and appropriate use of all PPE, not only masks, which requires correct and rigorous behavior from health care workers, particularly in doffing procedures and hand hygiene practices. WHO also recommends staff training on these recommendations, as well as the adequate procurement and availability of the necessary PPE and other supplies and facilities. Finally, WHO continues to emphasize the utmost importance of frequent hand hygiene, respiratory etiquette, and environmental cleaning and disinfection, as well as the importance of maintaining physical distances and avoidance of close, unprotected contact with people with fever or respiratory symptoms




Source: World Health Organization
https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations

Publised By: Snehith