How to welcome a guest for a few days during Covid-19 if one is vulnerable?

It is a bit risky to host a visitor in one's own home (nanny, friends, homestay, hosting refugees, etc.) during the COVID-19 epidemic...and to keep them your house for several days. We can, rightly, fear that they will contaminate us. And if the coronavirus is present in our home without our knowledge, they are the one at risk of being infected.

Here are some practical precautions based on scientific knowledge that can limit the risk, without cancelling it out (this is impossible): those who are frail (elderly or with risk factors) will apply them more carefully and rigorously.

First of all, if the guest is sick (fever and cough suggestive of COVID-19), or if you are sick yourself, it is prudent to cancel the invitation. If no one has any symptoms, however, contamination is still possible: in fact, half of virus carriers are asymptomatic, and it is during the two days preceding their illness that a sick person is most contagious. See the question How long is a person contagious?

Second, contamination is mostly "live" through the particles emitted by one and received by the other, face to face. When we talk to each other, it is therefore prudent to keep the mask on, or to stay at a great distance (more than 2 meters). Contamination is also caused by aerosols emitted while breathing (similar to the cigarette smoke of a smoker), and finally more rarely by viruses deposited by the saliva on objects, and recovered by one's hands then carried to their nose and eyes. See the question How does COVID-19 get caught?

• Prepare your guest's room one day in advance (more if possible): Over time, any virus will gradually disappear. It dies fairly quickly in the air and on porous, blotting objects (complete elimination on paper and cotton in 3 hours to 24 hours), but less quickly on smooth objects (virus inactivated in 3 to 5 days on stainless steel, glass or plastic). After 24 hours, the number of viruses is already divided by 100 or 1000 on almost all types of surfaces, which is enough to protect your guest.
• At a reception, if you are outside or in a large (>8 m2) and/or well-ventilated room (2 open windows), remain apart from each other to talk in order to each other without masks. If the room is small and/or poorly ventilated, it is better to keep the masks on. Avoid touching yourself or passing objects (e.g., bag, suitcase, telephone). After the first warm welcome and the installation of the guest in his room, it is important to agree on sanitary precautions. If your guest does not have any, provide him/her with masks and a disinfectant (hydro-alcoholic spray or gel at 60% or more).
• In their room, the guest has no special precautions to take, but you will not enter unless you are masked. After their departure, you will wait at least 24 hours to enter, air, change the sheets, and clean. If someone returns to the room quickly, ventilate thoroughly and spray 70% alcohol on all the surfaces, especially door and furniture handles and the table surface. If you have a separate toilet and bathroom for the guest, this is ideal.
• If you share the bathroom with your guest. Flushing the toilet creates an aerosol that can contaminate because there are viruses in the stool. It is best to only flush the toilet after closing the lid, leave the door wide open afterwards (and even all the time), and spray alcohol on the seat and on the handles (door, flush). You may also decide to wear a mask in your toilet, if it is shared. A toilet-less bathroom is less risky: leave the door open (unless the bathroom vent is effective), and provide one glass of toothpaste per person in addition to personal towels. See the question Can the SARS-CoV-2 coronavirus be caught in the bathroom?
• Meals are contaminating, because it is difficult to be more than 2 meters away, and impossible to keep a mask on. If one of you is vulnerable, it is better to avoid eating together, at least the first few days: the guest can take a tray in his room. After 3 to 5 days, if no one is sick, it means that you were not contaminated at the beginning, so you can lower your guard a little if there was no risk of contamination afterwards.

For a shared meal, put a cotton tablecloth on the table (it decontaminates quickly and is easy to wash), keep your distance (ideally 2 meters or more), and avoid talking loudly or upwards (so that any droplets from your mouth will fall onto your own plate). The ideal is to eat outside, otherwise it is good to air the room as much as possible during the meal (and keep warm clothes while eating). If objects (dishes, cutlery) are passed around, you can grab them with a paper towel, or decontaminate your hands afterwards.

So far, no food contamination has been published, so it is likely that this is not an important route. However, the person who prepares and serves the meal will wash their hands thoroughly before and during preparation, and it is best to wear a mask, as is done in collective kitchens. Washing dishes with hot water and detergent, or washing them in a washing machine, will remove the virus well. See the question How to organize a meal at home without risk for the guests?

The guest will be left with a drink glass and some cutlery, which they will not need to wash thoroughly each time they use it.

Finally, everyone will be careful not to contaminate themselves outside the household, and this is a point that must be explained to the guest to encourage them to keep their mask and distance when they go out, even when meeting friends: if they contaminate themselves, they are endangering the lives of the household!