Observation  Date  Interpretation  Supports Scenario 1?a  Supports Scenario 2?b
By 20 January, 198 laboratory-confirmed cases, 3 fatal, 25 recovered [28]  20 Jan 2020  Fatality risk among hospitalised cases is 11%c  Yes  Yes
No infections among the more than 700 people under medical surveillance, including HCWs [28]  20 Jan 2020  Very low human-to-human transmissibility  Yes  No (Note: assuming adequate contact tracing and surveillance)
Only one likely human-to-human cluster among the first 41 cases [18]  20 Jan 2020  Very low human-to-human transmissibility (R 0 of 0.02)  Yes  No (Note: assuming adequate contact tracing)
Only approximately 70% of the first 41 cases had exposure to Southern China Seafood Wholesale Market [16]  15 Jan 2020  Low human-to-human transmissibility (R 0 of 0.3)  Yes  No (Note: possible selection bias towards identifying cases linked to that market)
New cases with a travel history to Wuhan before onset were confirmed in other cities in China [29]  20 Jan 2020  Indicative of many mild to moderate infections (not requiring hospitalisation) in Wuhan  Yes  Yes
Four exported cases to other countries, all with relatively mild illness [30,31]  12–20 Jan 2020  Indicative of many mild to moderate infections not necessitating hospitalisation or outpatient medical care in Wuhan  Yes  Yes
Four exported cases, at least three of whom had no contact with Southern China Seafood Wholesale Market [30,31]  12–20 Jan 2020  At least some limited human-to-human transmission (unclear R 0)  Yes  Yes
Two family clusters in Guangdong, with family members who did not visit Wuhan but were infected after the other family member(s) returning from Wuhan were confirmed with the infection [29]  20 Jan 2020  At least some limited human-to-human transmission (unclear R 0)  Yes  Yes
15 HCWs confirmed with infection of 2019-nCoV (not clear whether infections were from one case or multiple cases) [20]  20 Jan 2020  Super-spreading event? Could still be consistent with limited human-to-human transmission if an isolated incident (unclear R 0)  Yes  Yes
Exported cases identified in Taiwan and the United States with illness onset dates on 11 and 19 January [32,33]  22 Jan 2020  Could be because of surveillance bias, but is more consistent with an increase in incidence of infections over time  No (Note: possible selection bias because of enhanced surveillance towards identifying more recent cases)  Yes