Can we catch COVID-19 without direct interaction with a contagious person?
Text updated on 2021-05-03
Yes, it is possible to catch the SARS-CoV-2 coronavirus through indirect contact, without interacting with an infected person. A few cases have been described. This mode of contamination seems to be rare.
COVID-19 is transmitted mainly by droplets and aerosols, and very rarely by contact with soiled surfaces (fomites). See the questions Is the SARS-CoV-2 coronavirus transmitted by aerosols? and How is COVID-19 caught? Droplets remain suspended in the air for only a few seconds, while aerosols can remain there for several hours. It is therefore possible to be contaminated by aerosols exhaled in an enclosed space by a contagious person without close interaction to that person.
A few cases of indirect transmission of coronavirus SARS-CoV-2 have been described, for example:
- 13 cases on a train while the infected person was off the train. In one of the cases, the infected person sat exactly where the contagious person was. In the other 12 cases, the infected person sat in the same row, or in one of the next two rows. The persons sitting in the next rows were not examined. Therefore, it would appear that these contaminations were aerosolized. The study does not specify the time elapsed between the passage of the infectious person and the infected person.
- a case in an airplane bathroom.
- a case on a bus in which a person with COVID-19 had left the bus 30 minutes earlier.
- a case in an elevator when the contagious person had taken the elevator two minutes before.
- a few cases in a hospital in South Africa, where the rooms of the infected person and the infected person were more than 6 meters apart. However, the authors of the study could not completely rule out transmission through health care workers.
- a few people were contaminated by the pipes that connected their bathroom to another apartment where their neighbours were suffering from COVID-19. The project is being carried out in South Korea, Hong Kong and Guangzhou, China.
These cases of indirect transmission of COVID-19 represent a small fraction of the cases described compared to the many transmissions through close contact with a contagious person (by droplets and aerosols). Although they are more difficult to demonstrate and detect than cases of direct transmission through contact, they suggest that indirect transmission is rare but possible.
For the COVID-19No contamination involving delivery people and fomites dropped on deliveries has been reported to our knowledge. The US CDC considers that "touching a surface is not considered a common means of contamination".
In China, frozen products from abroad are tested for the SARS-CoV-2 coronavirus and at least 10 packages have tested positive. However, the presence of the virus' RNA does not mean that the virus is infectious and in sufficient quantity to infect a person. In addition, the coronavirus does not survive the acidity of the digestive tract, and no transmission of COVID-19 by ingestion of food was observed. See the question Can the coronavirus SARS-CoV-2 be caught by eating?
If contamination from contaminated objects is rare, why continue to wash your hands and avoid touching your face? Because handwashing is a basic rule of hygiene that protects against many pathogens and prevents their spread. Coronavirus is not the only pathogen in life!
In conclusion, if you enter a place that has been visited by others before, ventilate as much as possible and wear a mask. At home, don't forget to air out your space several times a day, even in winter!
A regularly updated Google document, written by more than a dozen American experts, containing general and practical information on the transmission of SARS-CoV-2 by aerosols. The length of time the coronavirus can remain in indoor air depends on the environment and is in the order of 1-2 hours. When outdoor air enters an indoor space, it mixes with the air already present indoors. Replacing aerosol-laden air in indoor spaces with outdoor air takes between 5 minutes and a few hours, depending on the location.FAQs on Protecting Yourself from COVID-19 Aerosol Transmission.
A detailed study of people who travelled by train between December 19, 2019 and March 6, 2020 in China revealed that 234 passengers were likely contaminated on the train. In at least 13 cases, the contamination occurred while the contagious individual was off the train. Those who were in the same row as the contagious individual were 10 times more likely to get the COVID-19 than those placed one or two rows down.Hu, Maogui, et al. "The risk of COVID-19 transmission in train passengers: an epidemiological and modelling study." Clinical Infectious Diseases (2020).
Very detailed study of the 310 passengers on a Milan-South Korea flight: medical check-up in the airport before departure, only the asymptomatic persons took the plane (11 symptomatic persons did not take the plane), masks mandatory for the whole duration of the flight except for the bathrooms, 14-day quarantine on arrival in Korea and medical follow-up during the 14 days, tests COVID-19. A 28-year-old was infected when she took off her mask to go to the bathroom on the flight from Milan to South Korea. This person had been quarantined for 3 weeks alone at her home in Italy before the flight and had not used public transport to get to the airport. She had the first symptoms 8 days after the flight. On the plane, she used the same bathroom as a pre-symptomatic person (tested positive 2 days after the flight). The 18 cabin crew and medical personnel were not contaminated. They all wore masks.Bae, S. H., Shin, H., Koo, H. Y., Lee, S. W., Yang, J. M., & Yon, D. K. Asymptomatic Transmission of SARS-CoV-2 on Evacuation Flight. Emerging infectious diseases, 26(11).
One person became infected by riding a bus that had been carrying a person with COVID-19 who had left the bus 30 minutes earlier.Chen, S. (2020) Coronavirus can travel twice as far as official 'safe distance' and stay in air for 30 minutes, Chinese study finds. South China Morning Post. 9 March 2020.
In January-February 2020 in Guangzhou, China, a person was infected by entering an elevator in which an individual, who later tested positive for the SARS-CoV-2 coronavirus, had entered two minutes before. Neither person was wearing a mask and they both pressed the same elevator button. It is not known whether the contamination was indirect through contact with the elevator button or through the inhalation of aerosols.Xie, C., Zhao, H., Li, K., Zhang, Z., Lu, X., Peng, H., ... & Gu, Y. (2020). The evidence of indirect transmission of SARS-CoV-2 reported in Guangzhou, China. BMC public health, 20(1), 1-9.
In a hospital in South Africa, in March-April 2020, patients with COVID-19 contaminated other patients who were in remote rooms. The investigation suggests that some cases of coronavirus transmission may have occurred through contaminated objects. Patient P1 appears to have contaminated patient P3 when they were approximately 6 metres apart and for only 3 hours.Lessells, R., Moosa, Y., & De Oliveira, T. (2020). Report into a nosocomial outbreak of coronavirus disease 2019 (COVID-19) at Netcare St. Augustine's Hospital.
Two couples were infected because they lived in two apartments above an apartment where several people were infected with COVID-19. The three families did not know each other, and had not shared elevators during the contagion period. The investigation suggests that the contamination took place through flushing the toilets, which released aerosols that travelled through the drainage system and ended up in the bathrooms of the apartments. It is likely that the water from the U-shaped drainage traps under the bathtub had evaporated (as the bathtub is not used regularly) and therefore there was no longer a seal between the apartments. In addition, the two couples who were infected never opened their bathroom windows.Kang, M., Wei, J., Yuan, J., Guo, J., Zhang, Y., Hang, J., ... & Peng, X. (2020). Probable evidence of fecal aerosol transmission of SARS-CoV-2 in a high-rise building. Annals of internal medicine.
At the Heng Tai house on the Fu Heng estate in Hong Kong, a 59-year-old man living in apartment 13 on the 34th floor was likely infected with two people with COVID-19 who live in apartment 13 on the 32nd floor.Leung K., Leung C., Ho-him C. (2020) Coronavirus: at least 10 households evacuated from Hong Kong public housing block in Tai Po over multiple infections. South China Morning Post. Accessed on Dec 27 2020.
In the Luk Chuen building of Lek Yuen Estate in Hong Kong, four apartments in which 6 residents were infected - apartment #'s 710, 810, 1012, and 1112 on the 7th, 8th, 10th and 11th floors, respectively - were connected to the apartment of the index patient, the first patient in the building who was infected with COVID-19, in apartment #812 on the 8th floor through interconnected vertical air drainage pipes.Tsang D., Ho-him C. (2020) Coronavirus: Hongkonger living in public housing at centre of infection cluster confirmed as infected. South China Morning Post. 13 June 2020. Accessed on Dec 27 2020.
Compilation of 152 super-propagating events from COVID-19: an analysis of the table provided by the authors indicates that more than 95% of the cases are indoor transmissions. For the remaining 5%, it is not clear whether transmission occurred outdoors.Leclerc, Q. J., Fuller, N. M., Knight, L. E., Funk, S., Knight, G. M., & CMMID COVID-19 Working Group. (2020). What settings have been linked to SARS-CoV-2 transmission clusters?. Wellcome Open Research, 5(83), 83. Compilation.
In the United States, the National Center for Disease Control and Prevention (CDC) has updated its page on the subject explaining that "touching a surface is not considered a common means of contamination".CDC. COVID-19 Frequently Asked Questions. Last Accessed Dec 6, 2020.
The European CDC (European Centre for Disease Prevention and Control) mentions that "Indirect transmission through fomites that have been contaminated by respiratory secretions is considered possible, although so far, transmission through fomites has not been documented".ECDC. Transmission of COVID-19. Last Accessed Dec 6, 2020.
Article of 20 November 2020 taking stock of the state-of-the-art omg frozen products and the associated risk of transmission of COVID-19.Siregar, T. Could frozen food transmit... COVID-19? The Conversation. 20 Nov 2020. Last accessed 6 Dec 2020.
In a building in Seoul, people in 7 apartments were contaminated within a few days of each other. These people did not know each other and the 7 apartments shared bathroom drains.Hwang, S. E., Chang, J. H., Bumjo, O., & Heo, J. (2020). Possible Aerosol Transmission of COVID-19 Associated with an Outbreak in an Apartment in Seoul, South Korea, 2020. International Journal of Infectious Diseases.
Study showing indirect aerosol transmission in the New Zealand entry quarantine hotel. PCR testing took place in the poorly ventilated corridor of the hotel. Some travellers were contaminated by aerosols from infected persons who were standing in the corridor. These people were not present in the corridor at the same time.Eichler, N., Thornley, C., Swadi, T., Devine, T., McElnay, C., Sherwood, J., ... & Geoghegan, J. L. (2021). Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 during Border Quarantine and Air Travel, New Zealand (Aotearoa). Emerging Infectious Diseases, 27(5).