I am writing about COVID-19 contact tracing in the context of college opening plans. I think many people are not familiar with what a powerful tool contact tracing is, when combined with isolation of infected people and quarantine of exposed people. I spent 35 years working in disease control in public health departments, and am quite familiar with how contact tracing, isolation and quarantine work for control of transmission of tuberculosis, syphilis, and various vaccine-preventable diseases — most often in combination with curative and preventive treatment. The challenge is a bit greater with a disease that has no definitive treatment. On the other hand, isolation of the sick and quarantine of the exposed did work to control SARS worldwide.
Here’s how I think it is supposed to work, as applied to a residential college campus. I think it likely that, in spite of the two weeks of home quarantine before returning to campus, some students will test positive for COVID-19 upon arrival on campus (day zero). They will be isolated immediately, so that they don’t infect anyone else. They will get a thorough contact interview, to identify their close contacts (defined as being within six feet of an infectious person for at least 15 minutes) in the couple of days between arrival on campus and the receipt of results. A good contact interview should be done face to face, and includes review of personal calendars, address books, friend lists and social media posts, especially photographs.
Identified contacts will be put in quarantine, so that if they are in fact infected they won’t expose anyone else. That means they should be staying home, or in a quarantine facility, and having face-to-face contact with no-one.
Probably some students who tested negative on day 0 will test positive on day 6. These students will also be interviewed and their contacts elicited — there may be more such contacts, since the infected students have had six to seven days on campus already — and those contacts will be put in quarantine, so that if they are infected and become infectious they won’t expose anyone. Contacts from either the first or the second round of testing will be monitored for symptoms, and will (I hope) all be tested for COVID-19 when first quarantined and again some time later.
Rinse and repeat. After just a couple of rounds of testing, isolation and quarantine, it should be possible to eradicate transmission among students. One way to tell whether the overall system (including elimination of visitors to campus and off-campus travel) is working is to monitor the fraction of newly-identified infected students who were NOT identified as contacts during interviews of earlier infected students. It should be close to zero if the system is working as designed.
This process can and will work if carried out with vigor and full cooperation. Breaches in isolation or quarantine, breaches in the bans on visitors and off-campus travel, evasion of testing, unauthorized student gatherings, laboratory error or delays, failure to identify all contacts during contact interviews, failure to use masks when indicated, failure to locate contacts, and perhaps other failures I haven’t thought of, would undermine the effectiveness of the system and lead to unnecessary and perhaps unacceptable levels of disease. Such a system does not have to be absolutely perfect to be effective, but it does need to be pursued diligently and needs the cooperation of all concerned.
A few cases among students early in the term would not be a reason by itself to close a campus; but an inability to control the spread of infection among students with the disease-control tools available might be such a reason.
After this initial period of testing, isolation and quarantine, when campus life returns to something closer to the status quo ante, the residents and employees of the campus will be subject to the same risk — currently very low — of infection as everyone else in the community.
Richard S. Hopkins 
M.D., M.S.P.H.
Middlebury