Epidemic Intelligence Center, Taiwan Centers for Disease Control, Taipei, Taiwan.
Institute of Epidemiology and Preventive Medicine, National Taiwan University College of Public Health, Taipei, Taiwan.
JAMA Intern Med. 2020 Sep 1;180(9):1156-1163. doi: 10.1001/jamainternmed.2020.2020.
IMPORTANCE: The dynamics of coronavirus disease 2019 (COVID-19) transmissibility are yet to be fully understood. Better understanding of the transmission dynamics is important for the development and evaluation of effective control policies. OBJECTIVE: To delineate the transmission dynamics of COVID-19 and evaluate the transmission risk at different exposure window periods before and after symptom onset. DESIGN, SETTING, AND PARTICIPANTS: This prospective case-ascertained study in Taiwan included laboratory-confirmed cases of COVID-19 and their contacts. The study period was from January 15 to March 18, 2020. All close contacts were quarantined at home for 14 days after their last exposure to the index case. During the quarantine period, any relevant symptoms (fever, cough, or other respiratory symptoms) of contacts triggered a COVID-19 test. The final follow-up date was April 2, 2020. MAIN OUTCOMES AND MEASURES: Secondary clinical attack rate (considering symptomatic cases only) for different exposure time windows of the index cases and for different exposure settings (such as household, family, and health care). RESULTS: We enrolled 100 confirmed patients, with a median age of 44 years (range, 11-88 years), including 44 men and 56 women. Among their 2761 close contacts, there were 22 paired index-secondary cases. The overall secondary clinical attack rate was 0.7% (95% CI, 0.4%-1.0%). The attack rate was higher among the 1818 contacts whose exposure to index cases started within 5 days of symptom onset (1.0% [95% CI, 0.6%-1.6%]) compared with those who were exposed later (0 cases from 852 contacts; 95% CI, 0%-0.4%). The 299 contacts with exclusive presymptomatic exposures were also at risk (attack rate, 0.7% [95% CI, 0.2%-2.4%]). The attack rate was higher among household (4.6% [95% CI, 2.3%-9.3%]) and nonhousehold (5.3% [95% CI, 2.1%-12.8%]) family contacts than that in health care or other settings. The attack rates were higher among those aged 40 to 59 years (1.1% [95% CI, 0.6%-2.1%]) and those aged 60 years and older (0.9% [95% CI, 0.3%-2.6%]). CONCLUSIONS AND RELEVANCE: In this study, high transmissibility of COVID-19 before and immediately after symptom onset suggests that finding and isolating symptomatic patients alone may not suffice to contain the epidemic, and more generalized measures may be required, such as social distancing.
重要性： 2019 年冠状病毒病（COVID-19）的传播动力学尚未完全了解。更好地了解传播动力学对于制定和评估有效的控制政策非常重要。
目的：描绘 COVID-19 的传播动态，并评估症状出现前后不同暴露窗口期的传播风险。
设计、地点和参与者：这项在台湾进行的前瞻性病例确定研究包括 COVID-19 的实验室确诊病例及其接触者。研究期间为 2020 年 1 月 15 日至 3 月 18 日。所有密切接触者在最后一次接触指数病例后在家中隔离 14 天。在隔离期间，任何相关症状（发烧，咳嗽或其他呼吸道症状）的接触者都需要进行 COVID-19 测试。最终随访日期为 2020 年 4 月 2 日。
主要结果和措施：不同暴露时间窗口的指数病例和不同暴露环境（例如家庭，家庭和医疗保健）的二次临床发病率（仅考虑症状病例）。
结果：我们共纳入 100 例确诊患者，中位年龄为 44 岁（范围为 11-88 岁），包括 44 名男性和 56 名女性。在他们的 2761 位密切接触者中，有 22 对配对的指数-二级病例。总体二级临床发病率为 0.7％（95％CI，0.4％-1.0％）。与接触后发病的患者相比，发病时间在症状出现后 5 天内开始的 1818 位接触者（发病率为 1.0％[95％CI，0.6％-1.6％]）的发病率更高。发病风险更高的是 299 位有明确的潜伏期接触者（发病率为 0.7％[95％CI，0.2％-2.4％]）。发病风险更高的是家庭（4.6％[95％CI，2.3％-9.3％]）和非家庭（5.3％[95％CI，2.1％-12.8％]）家庭接触者，而医疗保健或其他环境中的接触者发病率较低。发病风险在 40 至 59 岁（1.1％[95％CI，0.6％-2.1％]）和 60 岁及以上（0.9％[95％CI，0.3％-2.6％]）人群中更高。
结论和相关性：在这项研究中，COVID-19 在症状出现前后及出现时具有很高的传染性，这表明仅发现和隔离有症状的患者可能不足以控制疫情，可能需要采取更广泛的措施，例如社会隔离。
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