Coronavirus disease (COVID-19): Summary of assumptions

In order to develop technical guidance to support F/P/T public health authorities and front-line clinicians in health care settings respond to the novel coronavirus causing COVID-19, a number of assumptions were taken to develop interim guidance documents.  These assumptions are based on currently available scientific evidence and expert opinion and are subject to change as new information on transmissibility and epidemiology becomes available.  It is still to be determined how easily the virus spreads between people.

Table of contents

• Transmission
• Incubation period
• Risk
• Period of communicability
• Contamination of surfaces
• Reference documents
• Endnotes

Transmission

• Symptomatic cases of COVID-19 are causing the majority of transmission^{Endnote 1}.
• Person-to-person transmission is mostly^{Endnote 2} occurring via infectious respiratory droplets
• Respiratory droplets and contact transmission are considered to be the most important routes of transmission of COVID-19 viruses, but do not fully account for the occurrence of all COVID-19 cases, previously known as novel coronavirus pneumonia (NCP), and the reasons for the rapid spread of this virus.^{Endnote 3}
• The virus enters a person’s body either:
• by large respiratory droplets containing the virus that adhere to mucous membranes of a person’s eyes, nose or mouth, or
• by touching a surface or an object contaminated with the virus and then proceeding to touching one’s eyes, nose and mouth.
• A longer exposure time and a more severe illness with coughing likely increases the risk of exposure to the virus^{Endnote 4}.
• Airborne transmission is not known to be occurring in community settings (i.e., “routinely”)^{Endnote 5}.
• Performing an aerosol-generating medical procedure (AGMP) can generate aerosols capable of being inhaled^{Endnote 6}, and capable of spreading further in the air than respiratory droplets.
• AGMP include tracheal intubation, non-invasive ventilation, tracheotomy, cardiopulmonary resuscitation, manual ventilation before intubation, and bronchoscopy^{Endnote 7}.
• Fecal-oral and body fluid transmission of COVID-19 viruses could be occurring^{Endnote 8}
• COVID-19 RNA has been detected in the faeces of some infected patients but no live virus recovery has been achieved to date ^{Endnote 9}. Chinese scientists report evidence of an oral-fecal transmission route for COVID-19 viruses and show that, in hospitalized patients, viral RNA was found in anal swabs and in blood samples. The results of the study are the first to show COVID-19 viruses could be transmitted via respiratory, fecal-oral, or body fluid routes.
• Zoonotic transmission associated with the COVID-19 is possible^{Endnote 10}.
• Available evidence on the COVID-19 virus and previous experience with other coronavirus (MERS-CoV and SARS-CoV) and other respiratory viruses (e.g., avian influenza) and the linkage of early cases in China to a live animal market, suggest that there may be zoonotic transmission associated with COVID-19^{Endnote 11}.  At present, there is no evidence that companion animals or pets such as cats and dogs have been infected or have spread COVID-19 ^{Endnote 12}.

Incubation period

The incubation period is up to 14 days.

• Current estimates of the incubation period range from 0-14 days with median estimates of 5-6 days between infection and the onset of clinical symptoms of the disease. Based on information from other coronavirus diseases, such as MERS and SARS, the incubation period of COVID-19 could be up to 14 days. WHO recommends that the follow-up of contacts of confirmed cases is 14 days.^{Endnote 13}.

Risk

In the absence of infection prevention and control precautions including the consistent and appropriate use of personal protective equipment:

• Any person who is in close contact (within 2 metres) with a COVID-19 case experiencing respiratory symptoms (e.g., sneezing, coughing) is at risk of being exposed to potentially infective respiratory droplets.^{Endnote 14}
• AGMP have been associated with an increased risk of transmission of coronaviruses (SARS-CoV and MERS-CoV) by inhalation.
• A person who is in direct physical contact (e.g., kissing, touching contaminated skin/hands) with a person with COVID-19 is at risk of infection, via the transfer of the virus.
• A person who has contact with an inanimate object, such as contaminated surfaces and objects, which can serve as the vehicle for transmission of COVID-19 viruses, is at risk of infection.

Period of communicability

The period of communicability is not well understood and varies by type of coronavirus.  Detailed medical information from people infected is needed to determine the infectious period of COVID-19.

• It is possible that people infected with COVID-19 may be infectious before showing significant symptoms. However, based on currently available data, the people who have symptoms are causing the majority of virus spread ^{Endnote 15}.
• Cessation of symptoms indicate that the period of communicability is ending.
• Two consecutive negative laboratory test results, at least 24 hours apart, can be used to determine the end of the communicable period^{Endnote 16}

Contamination of surfaces

• COVID-19 viruses can survive on surfaces from several hours to days depending on several factors ^{Endnote 17}
• Data from laboratory studies on SARS-CoV and MERS-CoV have shown that stability in the environment depends on several factors including relative temperature, humidity, and surface type
• The virus is easily inactivated by using simple disinfectants^{Endnote 18} such as a diluted bleach solution prepared daily ^{Endnote 19}.

Reference documents:

• WHO EPI-WiN presentation deck. More information about COVID-19 public health implications.

• WHO. Advice on the use of masks in the community, during home care and in health care settings in the context of the novel coronavirus (2019-nCoV) outbreak.

• WHO Q&A on coronaviruses

• CDC Frequently Asked Questions and Answers

• WHO Q&A on infection prevention and control for health care workers caring for patients with suspected or confirmed 2019-nCoV

• Molecular and serological investigation of 2019-nCoV infected patients: implication of multiple shedding routes

• WHO recommendations to reduce risk of transmission of emerging pathogens from animals to humans in live animal markets

• WHO Clinical management of severe acute respiratory infection when novel coronavirus (2019-nCoV) infection is suspected

• Persistence of coronaviruses on inanimate surfaces and its inactivation with biocidal agents

• WHO Situation Report COVID-19

Endnotes