World Health Organization Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China.
Laboratory of Data Discovery for Health Limited, Hong Kong Science Park, New Territories, Hong Kong Special Administrative Region, China.
Clin Infect Dis. 2021 Sep 15;73(6):e1314-e1320. doi: 10.1093/cid/ciab271.
The relative contributions of asymptomatic, presymptomatic, and symptomatic transmission of severe acute respiratory syndrome coronavirus 2 have not been clearly measured, although control measures may differ in response to the risk of spread posed by different types of cases.
We collected detailed information on transmission events and symptom status based on laboratory-confirmed patient data and contact tracing data from 4 provinces and 1 municipality in China. We estimated the variation in risk of transmission over time and the severity of secondary infections by symptomatic status of the infector.
There were 393 symptomatic index cases with 3136 close contacts and 185 asymptomatic index cases with 1078 close contacts included in the study. The secondary attack rates among close contacts of symptomatic and asymptomatic index cases were 4.1% (128 of 3136) and 1.1% (12 of 1078), respectively, corresponding to a higher transmission risk from symptomatic cases than from asymptomatic cases (odds ratio, 3.79; 95% confidence interval, 2.06-6.95). Approximately 25% (32 of 128) and 50% (6 of 12) of the infected close contacts were asymptomatic from symptomatic and asymptomatic index cases, respectively, while more than one third (38%) of the infections in the close contacts of symptomatic cases were attributable to exposure to the index cases before symptom onset.
Asymptomatic and presymptomatic transmissions play an important role in spreading infection, although asymptomatic cases pose a lower risk of transmission than symptomatic cases. Early case detection and effective test-and-trace measures are important to reduce transmission.
尽管控制措施可能因不同类型病例传播风险的不同而有所差异，但严重急性呼吸综合征冠状病毒 2 的无症状、出现症状前和有症状传播的相对贡献尚未得到明确衡量。
我们根据中国 4 个省和 1 个直辖市的实验室确诊患者数据和接触者追踪数据，收集了有关传播事件和症状状况的详细信息。我们通过感染者的症状状况来估计随时间推移传播风险的变化以及继发感染的严重程度。
研究纳入了 393 例有症状的索引病例（3136 名密切接触者）和 185 例无症状的索引病例（1078 名密切接触者）。有症状和无症状索引病例的密切接触者的继发感染率分别为 4.1%（3136 名中的 128 例）和 1.1%（1078 名中的 12 例），这表明有症状病例的传播风险高于无症状病例（比值比，3.79；95%置信区间，2.06-6.95）。大约 25%（128 例中的 32 例）和 50%（12 例中的 6 例）的感染密切接触者来自有症状和无症状索引病例，而无症状病例的感染中，超过三分之一（38%）是由于与出现症状前的索引病例接触所致。
无症状和出现症状前的传播在传播感染方面发挥了重要作用，尽管无症状病例的传播风险低于有症状病例。早期发现病例和实施有效的检测与追踪措施对于减少传播非常重要。
