Editor’s note: The writer of this letter spent 35 years working as an epidemiologist in state health departments before retiring a few years ago.
Health Department Director Mark Levine and Gov. Phil Scott have been doing a good job communicating about the pandemic. There is, however, something they and others have not been emphasizing enough, in my epidemiologic opinion. Avoiding group events, wearing masks when unavoidably near other people, washing hands frequently and vigorously, and so on are indeed important. But the single best thing you can do to avoid infecting others is to stay home if you feel sick, and to go home immediately, with no side trips, if you start feeling sick while you are away from home.
Then you can call your doctor — after you get home — to review your illness, arrange for any needed medical care, and make plans to get tested for the virus that causes COVID-19. Don’t wait for the results of a COVID-19 test to isolate yourself if you are feeling sick. (If you are very sick you may of course need to go to an emergency department, and you should call ahead if at all possible.)
Similarly, children should not go to school if feeling poorly, and if they start feeling sick while at school they should be separated from their classmates and their parents should pick them up as soon as possible.
The rest of us — teachers, bosses, co-workers, spouses, children, roommates — need to be supportive of people who need to suddenly self-isolate while the nature of their illness is clarified.
I am being a little vague here about what “feeling sick” means, since the symptoms of COVID-19 can be so diverse (various combinations of fever, chills, cough, shortness of breath, muscle pain, sore throat, headache, fatigue, weakness, stomach upset, loss of sense of taste and smell, and so on). The important point is to not ignore what your body is telling you about a change in your health status.
Immediately isolating yourself if you feel poorly won’t prevent all transmission, because people may be somewhat infectious to others for a few days before they realize they are sick, and may even become infectious without developing symptoms. But if we can reduce transmission by half, we can make a tremendous impact on the dynamics of transmission. If we can reduce the average number of people infected by each infected person to less than 1, the outbreak will stop.
Richard S. Hopkins, MD, MSPH 
Middlebury