https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30607-3/fulltext#tbl2
盡管4月4日柳葉刀才刊發了這篇文章，其流行病學部分在二月份已經有報道（現在查不到了）。
兩位患者為夫妻，密切接觸而傳染。
己查明，在他們得病前後，有接觸史的數百人中，隻有兩例查出陽性。
先後接融過百餘名醫務人員，無一人感染。
這個流病調查結果，給CDC、白宮等官方機構提供了最初的決策依據：此毒不足道，盡在掌握中。
372 contacts of either Patient 1 or Patient 2 were identified. Public health investigators were able to assess exposure risk and actively monitor symptoms for 347 (93%) of the 372 contacts, including 222 (94%) of 236 contacts with exposure on or after the date of first positive specimen collection. There were 25 people that had insufficient contact information to complete active monitoring. None of these individuals were found to have emergency department visits with fever, cough, or shortness of breath using near real-time surveillance data received from regional acute care hospitals for 14 days after their last exposure. Data presented are for those actively monitored. Of these 347 contacts, 195 (56%) were health-care personnel and 152 (44%) were community members. Although the majority of monitored contacts (228 [66%] of 347) had low-risk exposures, 119 (34%) had exposures of medium risk or greater (table 2).
Although Patient 1 and 2 live together and were hospitalised in the same facility, and therefore shared several common contacts (65 shared community contacts from emergency department or outpatient waiting rooms and 28 health-care personnel who interacted with both patients), they also had many unique contacts. Patient 1 had 92 unique health-care personnel contacts and 16 unique community contacts, including one household contact (Patient 2). Patient 2 had 75 unique health-care personnel contacts and 71 unique community contacts, including 51 from outpatient waiting rooms.
The majority of contacts (303 [87%] of 347 total monitored contacts and 195 [88%] of 222 monitored contacts on or after the date of first positive specimen collection) did not develop symptoms consistent with PUI criteria. Additionally, surveillance data from Illinois acute care hospitals indicated that no asymptomatic monitored contacts or other contacts who could not be reached for active symptom monitoring presented to an emergency department with fever, cough, or shortness of breath during DOI 6–30.
During active symptom monitoring, 44 (13%) of 347 total contacts became PUIs, including 27 (12%) of 222 monitored contacts who had exposures on or after the date of first positive specimen collection.
As a household contact, Patient 2 was the only community member who had a high-risk exposure. He became a PUI and subsequently the only other patient with COVID-19 in this investigation. Of the remaining 43 PUIs, all tested negative for SARS-CoV-2 while symptomatic; 32 of these PUIs were health-care personnel and 11 were community contacts. Although 18 (41%) of 44 PUIs had low-risk exposures, 26 (59%) had exposures of medium risk or greater.
32 health-care personnel contacts who were not PUIs had one-time nasopharyngeal and oropharyngeal specimens collected 7–14 days after their highest-risk exposure. All of these exposures occurred on or after the date of first positive specimen collection of a patient with COVID-19. 21 (66%) of these asymptomatic health-care personnel had exposures of medium risk or greater. All were negative for SARS-CoV-2 at the time of testing.
