MMWR Morb Mortal Wkly Rep. 2020 Jun 5;69(22):680-684. doi: 10.15585/mmwr.mm6922e1.
From January 21 through February 23, 2020, public health agencies detected 14 U.S. cases of coronavirus disease 2019 (COVID-19), all related to travel from China (1,2). The first nontravel-related U.S. case was confirmed on February 26 in a California resident who had become ill on February 13 (3). Two days later, on February 28, a second nontravel-related case was confirmed in the state of Washington (4,5). Examination of four lines of evidence provides insight into the timing of introduction and early transmission of SARS-CoV-2, the virus that causes COVID-19, into the United States before the detection of these two cases. First, syndromic surveillance based on emergency department records from counties affected early by the pandemic did not show an increase in visits for COVID-19-like illness before February 28. Second, 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. Third, 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. Finally, the occurrence of three cases, one in a California resident who died on February 6, a second in another resident of the same county who died February 17, and a third in an unidentified passenger or crew member aboard a Pacific cruise ship that left San Francisco on February 11, confirms cryptic circulation of the virus by early February. These data indicate that sustained, community transmission had begun before detection of the first two nontravel-related U.S. cases, likely resulting from the importation of a single lineage of virus from China in late January or early February, followed by several importations from Europe. 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.
从 2020 年 1 月 21 日至 2 月 23 日，公共卫生机构在美国发现了 14 例 2019 年冠状病毒病（COVID-19）病例，所有病例均与来自中国的旅行有关（1,2）。首例非旅行相关的美国病例于 2 月 26 日在加利福尼亚州的一名居民中确诊，该居民于 2 月 13 日发病（3）。两天后，即 2 月 28 日，华盛顿州又确诊了第二例非旅行相关病例（4,5）。对四条证据线索的检查为了解 2019 年冠状病毒病（COVID-19）的病毒（SARS-CoV-2）在美国这两例病例之前进入美国的传入和早期传播的时间提供了深入的了解。首先，基于受大流行早期影响的县的急诊记录进行的综合征监测并未显示 2 月 28 日之前 COVID-19 样疾病就诊人数的增加。其次，从 1 月 1 日开始，对来自美国多个地点的大约 11000 个呼吸道标本进行的回顾性 SARS-CoV-2 检测，在 2 月 20 日之前均未检测到阳性结果。第三，对早期病例的病毒 RNA 序列的分析表明，1 月 18 日至 2 月 9 日期间，从中国直接或间接输入的单一谱系病毒在美国开始传播，随后从欧洲输入了几例 SARS-CoV-2。最后，三例病例的发生证实了病毒的隐匿传播，其中一例是加利福尼亚州一名于 2 月 6 日死亡的居民，第二例是该县另一名于 2 月 17 日死亡的居民，第三例是一艘于 2 月 11 日离开旧金山的太平洋游轮上的一名未确定身份的乘客或船员，这些病例表明病毒的隐匿传播发生在 2 月之前。这些数据表明，在检测到首例两例非旅行相关的美国病例之前，病毒的持续社区传播已经开始，这可能是由于 1 月底或 2 月初从中国输入了单一谱系病毒，随后又从欧洲输入了几例。2 月之后，COVID-19 在整个美国的广泛出现突出表明，强有力的公共卫生系统对于迅速应对新出现的传染病威胁非常重要。
