Background

The study objective was to conduct a systematic review and meta-analysis on the proportion of asymptomatic infection among coronavirus disease 2019 (COVID-19) positive persons and their transmission potential.

Methods

We searched Embase, Medline, bioRxiv, and medRxiv up to 22 June 2020. We included cohorts or cross-sectional studies which systematically tested populations regardless of symptoms for COVID-19, or case series of any size reporting contact investigations of asymptomatic index patients. Two reviewers independently extracted data and assessed quality using pre-specified criteria. Only moderate/high quality studies were included. The main outcomes were proportion of asymptomatic infection among COVID-19 positive persons at testing and through follow-up, and secondary attack rate among close contacts of asymptomatic index patients. A qualitative synthesis was performed. Where appropriate, data were pooled using random effects meta-analysis to estimate proportions and 95% confidence intervals (95% CI).

Results

Of 6,137 identified studies, 71 underwent quality assessment after full text review, and 28 were high/moderate quality and were included. In two general population studies, the proportion of asymptomatic COVID-19 infection at time of testing was 20% and 75%, respectively; among three studies in contacts it was 8.2% to 50%. In meta-analysis, the proportion (95% CI) of asymptomatic COVID-19 infection in obstetric patients was 95% (45% to 100%) of which 59% (49% to 68%) remained asymptomatic through follow-up; among nursing home residents, the proportion was 54% (42% to 65%) of which 28% (13% to 50%) remained asymptomatic through follow-up. Transmission studies were too heterogenous to meta-analyse. Among five transmission studies, 18 of 96 (18.8%) close contacts exposed to asymptomatic index patients were COVID-19 positive.

Conclusions

Despite study heterogeneity, the proportion of asymptomatic infection among COVID-19 positive persons appears high and transmission potential seems substantial. To further our understanding, high quality studies in representative general population samples are required.

中文翻译：

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COVID-19 阳性者中无症状感染者的比例及其传播潜力：系统评价和荟萃分析

背景

研究目的是对2019冠状病毒病（COVID-19）阳性者中无症状感染者的比例及其传播潜力进行系统回顾和荟萃分析。

方法

我们检索了截至 2020 年 6 月 22 日的 Embase、Medline、bioRxiv 和 medRxiv。我们纳入了队列或横断面研究，这些研究系统地测试了人群，无论其是否有 COVID-19 症状，或报告无症状指数患者的接触调查的任何规模的病例系列。两名评审员独立提取数据并使用预先指定的标准评估质量。仅纳入中等/高质量的研究。主要结果是检测时和随访期间COVID-19阳性者中无症状感染者的比例，以及无症状指数患者的密切接触者中的继发发病率。进行了定性合成。在适当的情况下，使用随机效应荟萃分析来汇总数据，以估计比例和 95% 置信区间 (95% CI)。

结果

在 6,137 项已确定的研究中，71 项在全文审查后进行了质量评估，28 项为高/中等质量并被纳入。在两项一般人群研究中，检测时无症状的 COVID-19 感染比例分别为 20% 和 75%；在三项针对接触者的研究中，这一比例为 8.2% 至 50%。在荟萃分析中，产科患者中无症状COVID-19感染的比例（95% CI）为95%（45%至100%），其中59%（49%至68%）通过随访仍无症状；在疗养院居民中，这一比例为54%（42%至65%），其中28%（13%至50%）通过随访仍无症状。传播研究的异质性太高，无法进行荟萃分析。在五项传播研究中，接触过无症状指数患者的 96 名密切接触者中有 18 名 (18.8%) COVID-19 呈阳性。

结论

尽管研究存在异质性，但 COVID-19 阳性者中无症状感染者的比例似乎很高，而且传播潜力似乎很大。为了进一步加深我们的理解，需要对具有代表性的一般人群样本进行高质量的研究。