Dipartimento di Fisica, Università degli Studi di Trento, Trento-Povo, Italy.
Istituto di Geriatria e Gerontologia, Azienda Ospedaliero-Universitarià Piazzale Gambuli 1, Perugia, Italy.
Infect Dis (Lond). 2020 Nov-Dec;52(12):866-876. doi: 10.1080/23744235.2020.1797157. Epub 2020 Jul 30.
The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to 101,739 confirmed cases, in Italy, as of March 30th, 2020. While the analogous event in China appears to be under control at the moment, the outbreaks in western countries are still at an early stage of development. Italy, at present, is playing a major role in understanding the transmission dynamics of these new infections and evaluating the effectiveness of control measures in a western social context.
We combined a quarantined model with early-stage development data in Italy (during the period February 20th-March 30th) to predict longer-term progression (from March 30th, till June 25th, 2020 in a long-term view) with different control measures. Due to significant variations in the control strategies, which have been changing over time, and thanks to the introduction of detection technologies leading to faster confirmation of the SARS-CoV-2 infections, we made use of time-dependent contact and diagnosis rates to estimate when the effective daily reproduction ratio can fall below 1. Within the same framework, we analyze the possible secondary infection event after relaxing the isolation measures.
We study two simplified scenarios compatible with the observation data and the effects of two stringent measures on the evolution of the epidemic. On one side, the contact rate must be kept as low as possible, but it is also clear that, in a modern developed country, it cannot fall under certain minimum levels and for a long time. The complementary parameter tuned is the transition rate of the symptomatic infected individuals to the quarantined class, a parameter I connected with the time = 1/δ needed to perform diagnostic tests. Within the conditions of the outbreak in Italy, this time must fall under 12-8 h in order to make the reproduction number less than 1 to minimize the case numbers. Moreover, we show how the same parameter plays an even more important role in mitigating the effects of a possible secondary infection event.
截至 2020 年 3 月 30 日，意大利爆发了严重急性呼吸综合征冠状病毒 2（SARS-CoV-2），确诊病例达 101739 例。虽然目前中国的疫情似乎已得到控制，但西方国家的疫情仍处于早期发展阶段。目前，意大利在了解这些新感染的传播动力学和评估西方社会背景下的控制措施的有效性方面发挥着重要作用。
我们将隔离模型与意大利（2 月 20 日至 3 月 30 日期间）的早期发展数据相结合，以预测在不同控制措施下的长期进展（从 3 月 30 日到 2020 年 6 月 25 日）。由于控制策略存在显著差异（这些策略一直在随时间变化），并且由于检测技术的引入使得 SARS-CoV-2 感染的确诊速度更快，因此我们使用时间相关的接触率和诊断率来估计有效日繁殖数何时可降至 1 以下。在同一框架内，我们分析了放松隔离措施后的可能二次感染事件。
我们研究了两种与观察数据和两种严格措施对疫情演变影响相兼容的简化情景。一方面，必须尽可能降低接触率，但在一个现代化的发达国家，接触率不可能长期保持在某个最低水平以下。调整的补充参数是有症状感染者向隔离类别的转移率，这是一个与完成诊断测试所需时间 = 1/δ相关的参数。在意大利疫情爆发的情况下，为了使繁殖数小于 1，从而将病例数降到最低，该时间必须在 12-8 小时以内。此外，我们还展示了同一参数在减轻可能的二次感染事件的影响方面起着更为重要的作用。
