Department of Epidemiology, Center for Communicable Disease Dynamics, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
Flowminder Foundation, Stockholm, Sweden.
Int J Epidemiol. 2018 Oct 1;47(5):1562-1570. doi: 10.1093/ije/dyy095.
Travel restrictions were implemented on an unprecedented scale in 2015 in Sierra Leone to contain and eliminate Ebola virus disease. However, the impact of epidemic travel restrictions on mobility itself remains difficult to measure with traditional methods. New 'big data' approaches using mobile phone data can provide, in near real-time, the type of information needed to guide and evaluate control measures.
We analysed anonymous mobile phone call detail records (CDRs) from a leading operator in Sierra Leone between 20 March and 1 July in 2015. We used an anomaly detection algorithm to assess changes in travel during a national 'stay at home' lockdown from 27 to 29 March. To measure the magnitude of these changes and to assess effect modification by region and historical Ebola burden, we performed a time series analysis and a crossover analysis.
Routinely collected mobile phone data revealed a dramatic reduction in human mobility during a 3-day lockdown in Sierra Leone. The number of individuals relocating between chiefdoms decreased by 31% within 15 km, by 46% for 15-30 km and by 76% for distances greater than 30 km. This effect was highly heterogeneous in space, with higher impact in regions with higher Ebola incidence. Travel quickly returned to normal patterns after the restrictions were lifted.
The effects of travel restrictions on mobility can be large, targeted and measurable in near real-time. With appropriate anonymization protocols, mobile phone data should play a central role in guiding and monitoring interventions for epidemic containment.
2015 年，为了控制和消灭埃博拉病毒病，塞拉利昂前所未有地大规模实施了旅行限制。然而，传染病旅行限制对流动性本身的影响仍然难以用传统方法来衡量。新的“大数据”方法利用移动电话数据，可以实时提供指导和评估控制措施所需的信息。
我们分析了塞拉利昂一家主要运营商在 2015 年 3 月 20 日至 7 月 1 日期间的匿名移动电话通话详细记录（CDR）。我们使用异常检测算法来评估 3 月 27 日至 29 日全国“居家”封锁期间旅行的变化。为了衡量这些变化的幅度，并评估区域和历史埃博拉负担的影响修饰，我们进行了时间序列分析和交叉分析。
常规收集的移动电话数据显示，塞拉利昂为期 3 天的封锁期间，人类流动性大幅下降。在 15 公里范围内，酋长管辖区之间迁移的个人减少了 31%，在 15-30 公里范围内减少了 46%，在 30 公里以上的范围内减少了 76%。这种影响在空间上高度不均匀，在埃博拉发病率较高的地区影响更大。限制解除后，旅行很快恢复到正常模式。
旅行限制对流动性的影响是巨大的，可以在接近实时的情况下进行有针对性和可衡量的控制。通过适当的匿名协议，移动电话数据应该在指导和监测传染病遏制干预措施方面发挥核心作用。
