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What should I do if I find out that I have recently been in contact with someone who has just tested positive?

Text updated on 2020-07-30


Assess the likelihood of being contaminated, and for a period of 14 days be careful not to contaminate others, especially the elderly. Also follow the official recommendations of the country you are in.

If you met someone and then a few days later you learned that this person has tested positive for the COVID-19 SARS-CoV-2 coronavirus, you may have been exposed. Fortunately, it is COVID-19 not so easy to catch it: on average, over the course of a person's illness and without taking any precautions, a sick person only infects three other people. It is therefore possible that you are not infected.

Here are our tips to minimize the risk of propagation:

1- Make an assessment of your interaction with this person Did you see her from afar, or did you talk to her up close? Were you outside, or in a closed, narrow, unventilated place? Did you stay more than three feet away, or did you touch her hands or exchange objects? Were you wearing a mask? Did this person shout or sing near you? Did you spend three minutes with them, or several hours? Your answers to these questions will give you an idea of the risk you took. See How COVID-19 does he or she get it? and What is close contact? to help you assess your risk. If it seems very high (close and prolonged contact), it is best to confine yourself for 14 days as if you were sick yourself. Otherwise, here are some tips, to be adapted according to how close you have been to the person who became ill.

2- Make a note in your diary of the day of the "contact", observe your state of health and start counting the days. On average, the infection COVID-19 occurs 4 or 5 days after the contact, so if you have no symptoms after 5 or 6 days, you may be a little relieved. However, there are wide variations between individuals: it is possible to start the disease at any time during the following "fortnight" (14 days). In addition, some people are asymptomatic: they have no symptoms but have a viral load that can infect others during these 14 days. Therefore, one has to wait the 14 days to be sure to have passed the 14 days.

3- During this time, pay special attention to your contacts, since you can be contagious at any time. Caution: even without symptoms you can be contagious. In general, infected people become contagious two to three days before developing the first symptoms of the disease, with a peak of "contagiousness" between 2 days before and 1 day after the onset of symptoms.

Finally, follow the official recommendations of the country you are in, and take a test if recommended. Official recommendations : France: https://solidarites-sante.gouv.fr/IMG/pdf/fiche_personne_contact.pdf
United Kingdom: https://www.nhs.uk/conditions/coronavirus-covid-19/testing-and-tracing/nhs-test-and-trace-if-youve-been-in-contact-with-a-person-who-has-coronavirus/


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Sources

Comparison of studies that were published on SARS-CoV-2 prior to the implementation of containment measures and that estimated the number of individuals contaminated on average by a single person. This number is estimated at 3.28.

Liu, Y., Gayle, A. A., Wilder-Smith, A., Rocklev, J. (2020). The reproductive number of COVID-19 is higher compared to SARS coronavirus. Journal of travel medicine.

This article, based on 100 COVID-19 patients and 2,761 people who had close contact with them, indicates that the risk of transmitting the virus is highest in the 5 days following the onset of symptoms and in the days preceding the onset of symptoms.

Cheng, H. Y., Jian, S. W., Liu, D. P., Ng, T. C., Huang, W. T., & Lin, H. H. (2020). Contact tracing assessment of COVID-19 transmission dynamics in Taiwan and risk at different exposure periods before and after symptom onset. JAMA Internal Medicine.

This article compares the interval between the onset of symptoms in 77 pairs of individuals, one of whom has been infected by the other (this is called the serial interval, estimated here at 5 to 6 days) with the mean incubation time of the disease. The authors deduce that individuals carrying the SARS-CoV-2 virus are contagious as early as 2 to 3 days before the onset of the first symptoms and that the peak of contagiousness is between 2 days before and 1 day after the onset of symptoms.

He, X., Lau, E. H., Wu, P., Deng, X., Wang, J., Hao, X., ... & Mo, X. (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature medicine, 1-4.

Based on 181 cases in China, it is observed that in 90% of cases the onset of symptoms occurs within 10 days of infection.

Lauer, S. A., Grantz, K. H., Bi, Q., Jones, F. K., Zheng, Q., Meredith, H. R., ... & Lessler, J. (2020). The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: estimation and application. Annals of internal medicine, 172(9), 577-582.

The contagion begins 2.3 days before the onset of symptoms, which themselves begin 5 days after infection on average, giving a latency period of 2.7 days.

He, X., Lau, E. H., Wu, P., Deng, X., Wang, J., Hao, X., ... & Mo, X. (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature medicine, 26(5), 672-675.

The study of the first 830 people with Alzheimer's disease COVID-19 in China indicates that patients begin to isolate themselves on average 2.9 days after the onset of the first symptoms. Although patients remain contagious when they are isolated, they no longer infect anyone if isolation is properly implemented. In this case, the contagion phase averages 4.9 days: 2 days of pre-symptomatic contagion until they are isolated, then 2.9 days after the onset of symptoms.

Liu, T., Hu, J., Kang, M., Lin, L., Zhong, H., Xiao, J., ... & Deng, A. (2020). Transmission dynamics of 2019 novel coronavirus (2019-nCoV).

In this study of 391 people with the disease COVID-19 and their 1286 close contacts in Shenzhen, China in January-February 2020, it was observed that patients begin to isolate themselves on average 4.6 days after the onset of the first symptoms, a period when they are 6.6 days at risk of infecting someone by adding the average 2 days of pre-symptomatic contagion.

Bi, Q., Wu, Y., Mei, S., Ye, C., Zou, X., Zhang, Z., ... & Gao, W. (2020). Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study. The Lancet Infectious Diseases.

Further reading

How does she get COVID-19 ?

What is close contact?

What is a superspreader event for COVID-19 ?

Can a person without symptoms infect others?

How long is a person contagious?

What are the symptoms of COVID-19 ?

Who are the vulnerable people?

How do you live with a vulnerable person?