Epidemiology, Biostatistics and Prevention Institute, University of Zurich, Zurich, Switzerland.
Department of Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, CA, United States.
JMIR Public Health Surveill. 2022 May 19;8(5):e35653. doi: 10.2196/35653.
Digital proximity tracing (DPT) aims to complement manual contact tracing (MCT) in identifying exposed contacts and preventing further transmission of SARS-CoV-2 in the population. Although several DPT apps, including SwissCovid, have shown to have promising effects on mitigating the pandemic, several challenges have impeded them from fully achieving the desired results. A key question now relates to how the effectiveness of DPT can be improved, which requires a better understanding of factors influencing its processes.
In this study, we aim to provide a detailed examination of the exposure notification (EN) cascade and to evaluate potential contextual influences for successful receipt of an EN and subsequent actions taken by cases and contacts in different exposure settings.
We used data from 285 pairs of SARS-CoV-2-infected cases and their contacts within an observational cohort study of cases and contacts identified by MCT and enrolled between August 6, 2020, and January 17, 2021, in the canton of Zurich, Switzerland. We surveyed participants with electronic questionnaires. Data were summarized descriptively and stratified by exposure setting.
We found that only 79 (58.5%) of 135 contacts using the SwissCovid app whose corresponding cases reported to have triggered the EN also received one. Of these, 18 (22.8%) received the EN before MCT. Compared to those receiving an EN after MCT (61/79, 77.2%), we observed that a higher proportion of contacts receiving an EN before MCT were exposed in nonhousehold settings (11/18, 61.1%, vs 34/61, 55.7%) and their corresponding cases had more frequently reported mild-to-moderate symptoms (14/18, 77.8%, vs 42/61, 68.9%). Of the 18 contacts receiving an EN before MCT, 14 (77.8%) took recommended measures: 12 (66.7%) were tested for SARS-CoV-2, and 7 (38.9%) called the SwissCovid Infoline. In nonhousehold settings, the proportion of contacts taking preventive actions after receiving an EN was higher compared to same-household settings (82%, vs 67%). In addition, 1 (9%) of 11 ENs received in the nonhousehold setting before MCT led to the identification of a SARS-CoV-2-infected case by prompting the contact to get tested. This corresponds to 1 in 85 exposures of a contact to a case in a nonhousehold setting, in which both were app users and the case triggered the EN.
Our descriptive evaluation of the DPT notification cascade provides further evidence that DPT is an important complementary tool in pandemic mitigation, especially in nonhousehold exposure settings. However, the effect of DPT apps can only be exerted if code generation processes are efficient and exposed contacts are willing to undertake preventive actions. This highlights the need to focus efforts on keeping barriers to efficient code generation as low as possible and promoting not only app adoption but also compliance with the recommended measures upon an EN.
International Standard Randomised Controlled Trial Number Registry 14990068; https://doi.org/10.1186/ISRCTN14990068.
数字接触者追踪（DPT）旨在通过识别接触者来补充手动接触者追踪（MCT），以防止 SARS-CoV-2 在人群中的进一步传播。尽管包括 SwissCovid 在内的几个 DPT 应用程序已经显示出对缓解大流行有很大的效果，但仍有几个挑战阻碍了它们充分实现预期的效果。一个关键问题是如何提高 DPT 的有效性，这需要更好地了解影响其过程的因素。
在本研究中，我们旨在详细检查暴露通知（EN）的传播过程，并评估成功接收 EN 后和接触者在不同暴露环境下采取的后续行动的潜在情境影响。
我们使用了 2020 年 8 月 6 日至 2021 年 1 月 17 日期间在瑞士苏黎世州通过 MCT 确定的病例和接触者的观察队列研究中的 285 对 SARS-CoV-2 感染病例及其接触者的数据。我们使用电子问卷对参与者进行了调查。数据采用描述性方法进行总结，并按暴露环境进行分层。
我们发现，在使用 SwissCovid 应用程序的 135 名接触者中，只有 79 名（58.5%）报告触发了 EN 的相应病例也收到了 EN。其中，18 名（22.8%）在 MCT 之前收到了 EN。与那些在 MCT 之后收到 EN 的接触者相比（61/79，77.2%），我们观察到在 MCT 之前收到 EN 的接触者中，更多的接触者是在非家庭环境中暴露的（11/18，61.1%，而 34/61，55.7%），其对应的病例更频繁地报告有轻到中度症状（14/18，77.8%，而 42/61，68.9%）。在 MCT 之前收到 EN 的 18 名接触者中，有 14 名（77.8%）采取了推荐的措施：12 名（66.7%）接受了 SARS-CoV-2 检测，7 名（38.9%）拨打了 SwissCovid 信息热线。在非家庭环境中，与同一家庭环境相比，接触者在收到 EN 后采取预防措施的比例更高（82%，67%）。此外，在 MCT 之前收到的 11 份 EN 中有 1 份（9%）导致接触者接受检测，从而发现了一名 SARS-CoV-2 感染病例。这相当于在非家庭环境中，每 85 次接触者接触病例，并且这两个病例都是应用程序的使用者，且病例触发了 EN，就会发现一例感染病例。
我们对 DPT 通知级联的描述性评估进一步证明，DPT 是缓解大流行的重要补充工具，特别是在非家庭暴露环境中。然而，只有在代码生成过程有效且接触者愿意采取预防措施的情况下，DPT 应用程序的效果才能发挥出来。这突显出，我们需要集中精力尽可能降低有效代码生成的障碍，并不仅要促进应用程序的采用，还要促进在收到 EN 后遵守推荐措施。
国际标准随机对照试验注册号 14990068；https://doi.org/10.1186/ISRCTN14990068。
