⚠️New report on early spread: Four separate lines of evidence (syndromic surveillance, virus surveillance, phylogenetic analysis, & retro ID) suggest that limited U.S. community transmission likely began in late Jan / early Feb. Why important?... thread🧵 cdc.gov/mmwr/volumes/6…
2) Until late Feb, COVID-19 incidence was too low to be detected by normal emergency department syndromic surveillance for COVID-19–like illness. ➡️ our normal surveillance was completely inadequate. We had really needed to do more earlier testing.
3) “retrospective SARS-CoV-2 testing of approximately 11,000 respiratory specimens from several U.S. locations beginning January 1 identified no positive results before February 20.” ➡️ this backwards testing of passively collected samples also was insufficient!
4) “analysis of viral RNA sequences from early cases suggested that a single lineage of virus imported directly or indirectly from China began circulating in the United States between January 18 and February 9, followed by several SARS-CoV-2 importations from Europe.”
5) “the occurrence of three cases, one in a CA resident who died on Feb 6, a second in another resident of same county who died Feb 17, and third in an unidentified passenger or crew aboard a 🛳 that left SF on Feb 11, confirms cryptic circulation of the virus by early Feb.”
6) The widespread emergence of COVID-19 throughout the United States after February highlights the importance of robust public health systems to respond rapidly to emerging infectious threats
This figure puts the timelines into perspective. Relying on passive surveillance and ER surveillance was inadequate. Evidence shows we needed to have started community wide testing much earlier than relying on ER passive surveillance. 
