Mvolz answers Is there any value in self-quarantine (from Coronavirus), if you live with other people who aren’t taking similar precautions?

• Thinking about it with a toy model:

Assume you on average contact 25 people a day when you go out, and each of your housemates each also contacts 25 people a day. Also assume if they become ill, you’re 100% likely to get it from them. (These are not necessarily realistic assumptions, so please don’t infer anything from these particular numbers!)

This means that if you go out, you’re effectively contacting 100 people a day (75 of these by proxy.) If you stay home you’re reducing your total number of effective contacts from 100 to 75, so a 25% reduction. This is still an overall reduction in your total exposure.

Whether that reduction will be enough for you for it be worthwhile depends a lot on the specific numbers. These numbers include the overall risk of infection per contact (at present likely low but could increase, also depends a lot on where you live), how many contacts you and your housemates actually have, and the probability of getting it from them if they do get infected (probably a lot less than the 100% assumed here).

• My plan would be to not leave my room, except to take out the trash and to go to the bathroom. And I would shift to any early schedule. So I shouldn’t have much contact with my housemates, and would be doing my best not to touch the items they touch (and maybe disinfecting doorknobs /​ bathroom stuff before I touch them, if that’s practical).

So the factor that I’m most interested in is the one you assumed was 100%: if one of my housemates contracts the disease, how likely am I to catch it, and how much can I reduce the probability?

• That factor is called the secondary attack rate; I’ve seen values ranging from as low as 10% in one study (which has garnered a lot of scepticism) and in some larger studies, ~ 40%.

Preventing transmission in a shared space is very difficult. I can’t give specific estimates as to how much any of the measures you mentioned would reduce that likelihood, unfortunately.