(1/16) First, regardless of one's politics, I am confident we can all at least agree that we don't desire a bad clinical outcome for any member of our society.

If accurate, the timeline below is very instructive. It illustrates the imperfect nature of our current testing. https://twitter.com/DrEricDing/status/1311936166204256260

(2/16) This topic was broadly reviewed in this excellent article by my colleagues @AxellHouse and @EvaClarkMD: https://www.sciencedirect.com/science/article/pii/S0163445320305776?via%3Dihub

(3/16) The current unanswered sociological question is, What is the psychological effect of a negative test result? What fraction of people will let down their guard regarding masking and physical distancing because they have been told they have a negative test?

(4/16) We are all currently guessing about the answer to this question, but it is a testable question and testable hypothesis.

(5/16) The purpose of universal masking and physical distancing is precisely because we do not know who at any given time is theoretically in the 1-2 days prior to symptom onset.

For contact tracing purposes a close contact is defined as:

(6/16) Any individual who was within 6 feet of an infected person for at least 15 minutes starting from 2 days before illness onset (or, for asymptomatic patients, 2 days prior to positive specimen collection) until the time the patient is isolated. https://www.cdc.gov/coronavirus/2019-ncov/php/contact-tracing/contact-tracing-plan/contact-tracing.html

(7/16) Asymptomatic contacts of patients with confirmed #COVID19 should self-quarantine for 14 days from the time of last contact with someone during their infectious period. That is the current @CDC recommendation, with or without a negative test result.

(8/16) "Asymptomatic contacts testing negative should self-quarantine for 14 days from their last exposure (i.e., close encounter with confirmed or probable COVID-19 case)" https://www.cdc.gov/coronavirus/2019-ncov/php/contact-tracing/contact-tracing-plan/contact-tracing.html

(9/16) Suppose we run a thought experiment in which we tested everyone in the country today. We would catch some number of people who are positive and are asymptomatic. These people should self-isolate as appropriate.

(10/16) We would also have a large number of negative tests. There would be some number of these people who would theoretically be 1-2 days out from symptom onset yet have a negative test because of the diagnostic inaccuracy of our current tests, including PCR and antigen tests.

(11/16) From basic statistics, a test with relatively lower sensitivity can perform well in terms of negative predictive value if the prevalence of the disease is low. However, NPV won't be 100%.

(12/16) So, everyone who receives a negative test result should still practice universal physical distancing and masking when interacting with people outside their home. The negative test does not obviate the need for this because we don't know who is in the presymptomatic phase.

(13/16) Even a fraction of people who receive a negative test and are in the presymptomatic period could easily spread infection to a large number of people if public health measures are not followed.

(14/16) This case illustrates the inherent inaccuracy of testing, which in the real world can occur because of sample collection, actual analytical sensitivity, sample transport, etc.

(15/16) Finally, we don't know broadly the psychological impact of receiving a negative test result and the effects on behavior. This could be systematically studied.

(16/16) I would love feedback on this train of thought. Certainly I may have missed something.

@Cortes_Penfield @EvaClarkMD @JillWeather @A_Spallonii @TeenaXuMD @PaulSaxMD @dr_dmorgan @VPrasadMDMPH @BradSpellberg

@sargsyanz