Big challenge to learn performance (sens/spec) of various #COVID19 tests, which vary by test method, by site tested (NP, OP, sputum, trach aspirate/BAL) and perhaps most importantly by day from symptom onset when testing is performed. 1/3 https://twitter.com/dr_dmorgan/status/1244604750403792902

Also pertinent: why is the testing done? To dx #COVID19, or to guide transmission prevention approach (or both)? e.g. on day 8 an NP/OP sample may be less sensitive for dx but might be a reasonable guide to transmission risk (RT-PCR has very low LOD), as recent data...2/3

...suggest that by day 7 of illness the upper resp shedding and environmental contamination have greatly decreased, with lower respiratory sampling higher yield after days 5-7 in those ill enough to require hospital admission. 3/3