Coronavirus disease (COVID-19): Summary of assumptions
Updated: April 13, 2020
In order to develop technical guidance to support F/P/T public health authorities and front-line clinicians in health care settings responding 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.
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 transmissionFootnote 1; however many people with COVID-19 have only mild symptoms, especially at the early stage of the disease, and can still transmit to other people.
- Asymptomatic and presymptomatic transmission of COVID-19 is occurring; however, it remains unclear if it is a major driver of transmission.Footnote 2, Footnote 3, Footnote 4, Footnote 5, Footnote 6, Footnote 7, Footnote 8, Footnote 9, Footnote 10, Footnote 11, Footnote 12, Footnote 13, Footnote 14, Footnote 15, Footnote 16, Footnote 17, Footnote 18, Footnote 19, Footnote 20, Footnote 21, Footnote 22, Footnote 23
- Person-to-person transmission is mostly 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 virusFootnote 24
- The virus enters a person's body:
- 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.Footnote 25
- Airborne transmission is not known to be occurring in community settings (i.e., "routinely").Footnote 26
- Performing or being present for an aerosol-generating medical procedure (AGMP) in health care settings, which can generate aerosols capable of being inhaledFootnote 27 and spreading further in the air than respiratory droplets increases risk of exposure to the virus
- AGMP include tracheal intubation, extubation, non-invasive ventilation, tracheotomy, cardiopulmonary resuscitation, manual ventilation before intubation, bronchoscopy, nebulizer therapy, and sputum induction.Footnote 28
- Fecal-oral and body fluid transmission of COVID-19 viruses could be occurringFootnote 29
- The risk of catching COVID-19 from feces of an infected person appears to be low. While initial investigations suggest the virus may be present in feces in some cases, spread through this route is not a considerable driver of this outbreak.
- Zoonotic transmission associated with the COVID-19 is possible.Footnote 30
- Although the virus likely originated from a wild animal host, the virus has adapted to efficiently transmit from human-to-human. There is currently no evidence to suggest that animals, including companion animals or pets, are playing a role in the spread of COVID-19Footnote 31.
- Based on the limited data available on COVID-19 in pregnancy, there is currently no evidence of transmission of COVID-19 from mother to baby occurring during pregnancy or delivery.Footnote 32, Footnote 33
Incubation period
- The incubation period is up to 14 days.
- Current estimates of the incubation period range from 1-14 days with median estimates of 5-6 days between infection and the onset of clinical symptoms of the disease. WHO recommends that the follow-up of contacts of confirmed cases is 14 days.Footnote 34
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, even if mild, (e.g., sneezing, coughing) is at risk of being exposed to potentially infective respiratory droplets.Footnote 35
- 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 surfaces and objects contaminated with the virus, 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. Detailed information from people infected is needed to characterize onset and duration of viral shedding and determine the infectious period of COVID-19.
- It is possible that people infected with COVID-19 may be infectious before showing significant symptomsFootnote 2, Footnote 3, Footnote 4, Footnote 5, Footnote 6, Footnote 7, Footnote 8, Footnote 9, Footnote 10, Footnote 11, Footnote 12, Footnote 13, Footnote 14, Footnote 15, Footnote 16, Footnote 17, Footnote 18, Footnote 19, Footnote 20, Footnote 21, Footnote 22, Footnote 23. However, based on currently available data, the people who have symptoms are causing the majority of virus spread.Footnote 36
- For mild cases that do not require hospitalization, it is assumed that they are no longer communicable 10 days after onset of illness, as long as they are afebrile at that time and have improved clinically.Footnote 37, Footnote 38, Footnote 39, Footnote 40, Footnote 41, Footnote 42, Footnote 43, Footnote 44, Footnote 45 Absence of cough is not required for those known to have chronic cough or who are experiencing reactive airways post-infection.
- Two consecutive negative laboratory test results, at least 24 hours apart, can be used to determine the end of the communicable period.Footnote 46
Contamination of surfaces
- COVID-19 viruses can survive on surfaces from several hours to days depending on several factors.Footnote 47
- This may vary under different conditions such as surface type, relative temperature or humidity of the environment. The virus has been detectable up to four hours on copper, up to 24 hours on cardboard and up to two to three days on plastic and stainless steel.Footnote 48
- The virus is easily inactivated by using simple disinfectantsFootnote 49 such as store-bought disinfectants, and alternatively diluted bleach solution prepared daily.Footnote 50
Reference documents:
Centers for Disease Control and Prevention (CDC). CDC Frequently Asked Questions and Answers. 19 March 2020. Available from: https://www.cdc.gov/coronavirus/2019-ncov/faq.html
European Centre for Disease Prevention and Control (ECDC). Q & A on COVID-19. 6 Mar 2020. Available at: https://www.ecdc.europa.eu/en/novel-coronavirus-china/questions-answers
Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and its inactivation with biocidal agents. Journal of Hospital Infections. 2020 March; 104(3): 246-51.
WHO EPI-WiN presentation deck. More information about COVID-19 public health implications.
World Health Organization (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. 19 March 2020. Available from: https://www.who.int/publications-detail/advice-on-the-use-of-masks-the-community-during-home-care-and-in-health-care-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreak
World Health Organization (WHO). WHO Q&A on coronaviruses. 9 March 2020. Available from: https://www.who.int/news-room/q-a-detail/q-a-coronaviruses
World Health Organization (WHO). WHO Q&A on infection prevention and control for health care workers caring for patients with suspected or confirmed 2019-nCoV. 1 March 2020. Available from: https://www.who.int/news-room/q-a-detail/q-a-on-infection-prevention-and-control-for-health-care-workers-caring-for-patients-with-suspected-or-confirmed-2019-ncov
World Health Organization (WHO). WHO recommendations to reduce risk of transmission of emerging pathogens from animals to humans in live animal marks. 2020. Available at: https://www.who.int/health-topics/coronavirus/who-recommendations-to-reduce-risk-of-transmission-of-emerging-pathogens-from-animals-to-humans-in-live-animal-markets
World Health Organization (WHO). WHO Clinical management of severe acute respiratory infection when novel coronavirus (2019-nCoV) infection is suspected: Interim guidance. 13 March 2020. Available at: https://www.who.int/publications-detail/clinical-management-of-severe-acute-respiratory-infection-when-novel-coronavirus-(ncov)-infection-is-suspected
World Health Organization (WHO). Coronavirus disease 2019 (COVID-19) Situation Report - 30. Data as reported by 19 February 2020. Available at: https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200219-sitrep-30-covid-19.pdf?sfvrsn=3346b04f_2
Zhang E, Du RH, Li B, Zheng XS, Yang XL, Hu B, Wang YY, Xiao GF, Yan B, Shi ZL, Zhou P. Molecular and serological investigation of 2019-nCoV infected patients: implication of multiple shedding routes. Emerging Microbes & Infections. 2020 Feb; 9: 386-89.
Endnotes
- Footnote 1
-
WHO. Q&A on coronaviruses. [Online] 9 March 2020 [Accessed at: https://www.who.int/news-room/q-a-detail/q-a-coronaviruses].
- Footnote 2
-
He X, Lau EH, Wu P. et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. medRxiv preprint. 18 Mar 2020 [Accessed at: https://www.medrxiv.org/content/10.1101/2020.03.15.20036707v2]
- Footnote 3
-
Xia, W., Liao, J., Li, C. et al. Transmission of corona virus disease 2019 during the incubation period may lead to a quarantine loophole. medRxiv preprint. 8 Mar 2020 [Accessed at: https://www.medrxiv.org/content/10.1101/2020.03.06.20031955v1]
- Footnote 4
-
Rothe, C., Schunk, M., Sothmann, P. et al. Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. The New England Journal of Medicine. 5 Mar 2020 [Accessed at: https://www.nejm.org/doi/full/10.1056/NEJMc2001468]
- Footnote 5
-
Yu, P., Zhu, J., Zhang, Z. et al. A familial cluster of infection associated with the 2019 novel coronavirus indicating potential person-to-person transmission during the incubation period. The Journal of Infectious Diseases. 18 Feb 2020 [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/32067043]
- Footnote 6
-
Bai, Y., Yao, L., Wei, T. et al. Presumed asymptomatic carrier transmission of COVID-19. JAMA. 21 Feb 2020 [Accessed at: https://jamanetwork.com/journals/jama/fullarticle/2762028]
- Footnote 7
-
Hu, Z., Song, C., Xu, C. et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, china. medRxiv preprint. 25 Feb 2020 [Accessed at: https://www.medrxiv.org/content/10.1101/2020.02.20.20025619v2]
- Footnote 8
-
Tong, Z., Tang, A., Li, K. et al. Potential presymptomatic transmission of SARS-CoV-2, Zhejiang province, China, 2020. Emerging Infectious Diseases [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/32091386]
- Footnote 9
-
Wang, P., Lian, Z., Chen, Y. et al. Investigation of a cluster of 2019 novel coronavirus disease (COVID-19) with possible transmission during the incubation period - Shenyang City, China, 2020. China CDC Weekly, 2(8), 126.
- Footnote 10
-
Tang, A., Tong, Z., Wang, H. et al. Detection of novel coronavirus by RT-PCR in stool specimen from asymptomatic child, China. Emerging Infectious Diseases [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/32150527]
- Footnote 11
-
Covid-19 National Emergency Response Center, Epidemiology, Case Management Team, Korea Centers for Disease Control, & Prevention. Early epidemiological and clinical characteristics of 28 cases of coronavirus disease in South Korea. Osong Public Health and Research Perspectives [Accessed at: https://ophrp.org/journal/view.php?doi=10.24171/j.phrp.2020.11.1.03
- Footnote 12
-
Lu, S., Lin, J., Zhang, Z. et al. Alert for non-respiratory symptoms of coronavirus disease 2019 (COVID-19) patients in epidemic period: A case report of familial cluster with three asymptomatic COVID-19 patients. Journal of Medical Virology. 19 Mar 2020 [Accessed at: https://onlinelibrary.wiley.com/doi/abs/10.1002/jmv.25776]
- Footnote 13
-
Lui, X., Wu, J., Lui, M. et al. Presymptomatic transmission of COVID-19 in a cluster of cases occurred in confined space: A case report. 19 Mar 2020 [Accessed at: https://www.researchsquare.com/article/rs-18053/v1]
- Footnote 14
-
Li, P., Fu, J. B., Li, K. F. et al. Transmission of COVID-19 in the terminal stage of incubation period: A familial cluster. International Journal of Infectious Diseases. [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/32194239]
- Footnote 15
-
Qian, G., Yang, N., Ma, A. H. Y. et al. A COVID-19 transmission within a family cluster by presymptomatic infectors in china. Clinical Infectious Diseases. [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/32201889]
- Footnote 16
-
Kimball A., Hatfield K.M., Arons M. et al. Asymptomatic and presymptomatic SARS-CoV-2 infections in residents of a long-term care skilled nursing facility - King County, Washington, March 2020. MMWR Morb Mortal Wkly Rep. 27 Mar 2020 [Accessed at: https://www.cdc.gov/mmwr/volumes/69/wr/mm6913e1.htm?s_cid=mm6913e1_&deliveryName=USCDC_921-DM24113]
- Footnote 17
-
Mizumoto K., Kagaya K., Zarebski A., Chowell G. Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020. Euro Surveill.[Accessed at: https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2020.25.10.2000180]
- Footnote 18
-
Wölfel, R., Corman, V.M., Guggemos, W. et al. Virological assessment of hospitalized patients with COVID-2019. Nature. 1 April 2020 [Accessed at: https://www.nature.com/articles/s41586-020-2196-x]
- Footnote 19
-
Wei W.E., Li Z., Chiew C.J. et al. Presymptomatic Transmission of SARS-CoV-2 - Singapore, January 23-March 16, 2020. MMWR Morb Mortal Wkly Rep. 1 April 2020. [Accessed at: https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e1.htm#suggestedcitation]
- Footnote 20
-
Kluytmans, M., Buiting, A., Pas, S.et al. SARS-CoV-2 infection in 86 healthcare workers in two dutch hospitals in March 2020. medRxiv preprint. 31 Mar 2020 [Accessed at: https://www.medrxiv.org/content/10.1101/2020.03.23.20041913v3]
- Footnote 21
-
Gostic, K., Gomez, A. C., Mummah, R. O. et al. Estimated effectiveness of symptom and risk screening to prevent the spread of COVID-19. eLife. 24 Feb 2020 [Accessed at: https://elifesciences.org/articles/55570]
- Footnote 22
-
Nishiura H., Kobayashi T., Suzuki A. et al. Estimation of the asymptomatic ratio of novel coronavirus infections (COVID-19). International Journal of Infectious Diseases. 13 Feb 2020. https://www.ijidonline.com/article/S1201-9712(20)30139-9/pdf]
- Footnote 23
-
Chan, J. F., Yuan, S., Kok, K. H.et al. A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: A study of a family cluster. Lancet. [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/31986261]
- Footnote 24
-
Zhang, W., Du, R. Li, B. et al. Molecular and serological investigation of 2019-nCoV infected patients: implication of multiple shedding routes. Journal of Emerging Microbes & Infections. [Accessed at: https://www.tandfonline.com/doi/full/10.1080/22221751.2020.1729071]
- Footnote 25
-
CDC. Frequently Asked Questions and Answers. [Online] 19 March 2020 [Accessed at https://www.cdc.gov/coronavirus/2019-ncov/faq.html]
- Footnote 26
-
WHO. Q&A on infection prevention and control for health care workers caring for patients with suspected or confirmed 2019-nCoV. [Online] 1 March 2020 [Accessed at: https://www.who.int/news-room/q-a-detail/q-a-on-infection-prevention-and-control-for-health-care-workers-caring-for-patients-with-suspected-or-confirmed-2019-ncov].
- Footnote 27
-
Ibid.
- Footnote 28
-
Ibid.
- Footnote 29
-
Zhang, W., Du, R. Li, B. et al. Molecular and serological investigation of 2019-nCoV infected patients: implication of multiple shedding routes. Journal of Emerging Microbes & Infections. [Accessed at: https://www.tandfonline.com/doi/full/10.1080/22221751.2020.1729071]
- Footnote 30
-
WHO. WHO recommendations to reduce risk of transmission of emerging pathogens from animals to humans in live animal marks. [Online] February 13, 2020 [Accessed at: https://www.who.int/health-topics/coronavirus/who-recommendations-to-reduce-risk-of-transmission-of-emerging-pathogens-from-animals-to-humans-in-live-animal-markets].
- Footnote 31
-
OiE World Organisation for Animal Health. Questions and Answers on the 2019 Coronavirus Disease (COVID-19). [Online]. March 26, 2020 [Accessed at: https://www.oie.int/en/scientific-expertise/specific-information-and-recommendations/questions-and-answers-on-2019novel-coronavirus/].
- Footnote 32
-
Rothe, C., Schunk, M., Sothmann, P. et al. Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. The New England Journal of Medicine. 5 Mar 2020 [Accessed at: https://www.nejm.org/doi/full/10.1056/NEJMc2001468]
- Footnote 33
-
Zhang, W., Du, R. Li, B. et al. Molecular and serological investigation of 2019-nCoV infected patients: implication of multiple shedding routes. Journal of Emerging Microbes & Infections. [Accessed at: https://www.tandfonline.com/doi/full/10.1080/22221751.2020.1729071]
- Footnote 34
-
WHO. Coronavirus disease 2019 (COVID-19) Situation Report -59. [Online] 20 March 2020 [Accessed at https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200319-sitrep-59-covid-19.pdf?sfvrsn=c3dcdef9_2]
- Footnote 35
-
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. [Online] 21 February 2020 [Accessed at: https://www.who.int/publications-detail/advice-on-the-use-of-masks-the-community-during-home-care-and-in-health-care-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreak]
- Footnote 36
-
Ibid.
- Footnote 37
-
Zhang, I., Wan, K., Chen, J. et al. When will the battle against coronavirus end in Wuhan: a SEIR modeling analysis. medRxiv preprint. 18 February 2020 [Accessed at: https://www.medrxiv.org/content/10.1101/2020.02.16.20023804v1].
- Footnote 38
-
Read, J., Bridgen, J.R., Cummings, D.A., Novel coronavirus 2019-CoV: early estimation of epidemiological parameters and epidemic predictions. 31 January 2020. [Accessed at: https://www.publichealthontario.ca/-/media/documents/ncov/research-medrxiv-epidemiological-parameters.pdf?la=en]
- Footnote 39
-
Lin, H. Liu, W. Gao, H., et al. Trends in transmissibility of 2019 novel coronavirus infected pneumonia in Wuhan and 29 provinces in China. 2 Mar 2020 [Accessed at: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3544821&utm_source=EC&utm_medium=Connect]
- Footnote 40
-
You, C., Deng, Y., Hu, W., et al Estimation of the time-varying reproduction number of COVID-19 outbreak in China. medRxiv preprint. 17 February 2020. [Accessed at: https://www.medrxiv.org/content/10.1101/2020.02.08.20021253v2]
- Footnote 41
-
Li, R., Pei, S., Chen., B., et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus. 16 Mar 2020. [Accessed at: https://science.sciencemag.org/content/early/2020/03/24/science.abb3221]
- Footnote 42
-
Ding, Y., Luo, S., Zheng, X., et al. Association of population migration and coronavirus disease 2019 epidemic control. medRxiv preprint. 20 February 2020. [Accessed at: https://www.medrxiv.org/content/10.1101/2020.02.18.20024661v1]
- Footnote 43
-
Hu, Z., Song, C., Xu, C., et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. 4 Mar 2020. [Accessed at: https://www.ncbi.nlm.nih.gov/pubmed/32146694]
- Footnote 44
-
Ding, Y., Luo, S., Zheng, X., et al. Association of population migration and coronavirus disease 2019 epidemic control. medRxiv preprint. 20 February 2020. [Accessed at: https://www.medrxiv.org/content/10.1101/2020.02.18.20024661v1]
- Footnote 45
-
Wölfel, R., Corman., V., Guggemos, W., et al. Virological assessment of hospitalized cases of coronavirus disease 2019. medRxiv preprint. 5 Mar 2020. [Accessed at: https://www.medrxiv.org/content/10.1101/2020.03.05.20030502v1.full.pdf]
- Footnote 46
-
WHO. Clinical management of severe acute respiratory infection when novel coronavirus (2019-nCoV) infection is suspected. [Online] 13 March 2020 [Accessed at: https://www.who.int/publications-detail/clinical-management-of-severe-acute-respiratory-infection-when-novel-coronavirus-(ncov)-infection-is-suspected].
- Footnote 47
-
WHO. Q&A on infection prevention and control for health care workers caring for patients with suspected or confirmed 2019-nCoV. [Online] 21 February 2020 [Accessed at: https://www.who.int/news-room/q-a-detail/q-a-on-infection-prevention-and-control-for-health-care-workers-caring-for-patients-with-suspected-or-confirmed-2019-ncov ].
- Footnote 48
-
van Doremalen N, Bushmaker T, Morris DH. et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. The New England Journal of Medicine. [Accessed at: https://www.nejm.org/doi/full/10.1056/NEJMc2004973]
- Footnote 49
-
WHO. Q&A on coronaviruses. [Online] 21 February 2020 [Accessed at: https://www.who.int/news-room/q-a-detail/q-a-coronaviruses].
- Footnote 50
-
Kampf G, Todt D, Pfaender S, Steinmann E, Persistence of coronaviruses on inanimate surfaces and its inactivation with biocidal agents, Journal of Hospital Infection.https://doi.org/10.1016/j.jhin.2020.01.022 [Accessed at: https://www.sciencedirect.com/science/article/pii/S0195670120300463?via%3Dihub].
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