Department of Geography, 3141 Turlington Hall, University of Florida, Gainesville, Florida 32611-7315, USA.
Malar J. 2009 Dec 10;8:287. doi: 10.1186/1475-2875-8-287.
Malaria endemicity in Zanzibar has reached historically low levels, and the epidemiology of malaria transmission is in transition. To capitalize on these gains, Zanzibar has commissioned a feasibility assessment to help inform on whether to move to an elimination campaign. Declining local transmission has refocused attention on imported malaria. Recent studies have shown that anonimized mobile phone records provide a valuable data source for characterizing human movements without compromising the privacy of phone users. Such movement data in combination with spatial data on P. falciparum endemicity provide a way of characterizing the patterns of parasite carrier movements and the rates of malaria importation, which have been used as part of the malaria elimination feasibility assessment for the islands of Zanzibar.
Records encompassing three months of complete mobile phone usage for the period October-December 2008 were obtained from the Zanzibar Telecom (Zantel) mobile phone network company, the principal provider on the islands of Zanzibar. The data included the dates of all phone usage by 770,369 individual anonymous users. Each individual call and message was spatially referenced to one of six areas: Zanzibar and five mainland Tanzania regions. Information on the numbers of Zanzibar residents travelling to the mainland, locations visited and lengths of stay were extracted. Spatial and temporal data on P. falciparum transmission intensity and seasonality enabled linkage of this information to endemicity exposure and, motivated by malaria transmission models, estimates of the expected patterns of parasite importation to be made.
Over the three month period studied, 88% of users made calls that were routed only through masts on Zanzibar, suggesting that no long distance travel was undertaken by this group. Of those who made calls routed through mainland masts the vast majority of trips were estimated to be of less than five days in length, and to the Dar Es Salaam Zantel-defined region. Though this region covered a wide range of transmission intensities, data on total infection numbers in Zanzibar combined with mathematical models enabled informed estimation of transmission exposure and imported infection numbers. These showed that the majority of trips made posed a relatively low risk for parasite importation, but risk groups visiting higher transmission regions for extended periods of time could be identified.
Anonymous mobile phone records provide valuable information on human movement patterns in areas that are typically data-sparse. Estimates of human movement patterns from Zanzibar to mainland Tanzania suggest that imported malaria risk from this group is heterogeneously distributed; a few people account for most of the risk for imported malaria. In combination with spatial data on malaria endemicity and transmission models, movement patterns derived from phone records can inform on the likely sources and rates of malaria importation. Such information is important for assessing the feasibility of malaria elimination and planning an elimination campaign.
桑给巴尔的疟疾流行率已降至历史最低水平，疟疾传播的流行病学也正在发生转变。为了利用这些成果，桑给巴尔委托进行了一项可行性评估，以确定是否开展消除疟疾运动。随着当地传播的减少，人们的注意力重新集中在输入性疟疾上。最近的研究表明，匿名移动电话记录在不损害电话用户隐私的情况下，为描述人类活动提供了有价值的数据来源。这种移动数据与疟疾流行地区的空间数据相结合，为描述寄生虫携带者的活动模式和疟疾输入率提供了途径，这些信息已被用于桑给巴尔岛消除疟疾可行性评估的一部分。
2008 年 10 月至 12 月三个月内，我们从桑给巴尔电信（Zantel）移动电话网络公司获取了记录，该公司是桑给巴尔群岛的主要移动电话网络公司。数据包括 770369 名匿名用户的所有电话使用日期。每个电话和短信都被空间定位到六个地区之一：桑给巴尔和坦桑尼亚大陆的五个地区。提取了关于前往大陆的桑给巴尔居民人数、访问地点和停留时间的信息。疟原虫传播强度和季节性的时空数据使这些信息与流行地区接触情况相关联，并根据疟疾传播模型，对寄生虫输入的预期模式进行了估计。
在所研究的三个月期间，88%的用户只拨打通过桑给巴尔基站转接的电话，这表明该组人员没有进行长途旅行。在那些通过大陆基站转接的电话中，绝大多数旅行估计持续时间不到五天，而且是前往达累斯萨拉姆 Zantel 定义的区域。虽然该区域覆盖了广泛的传播强度，但结合数学模型，关于桑给巴尔总感染人数的数据可以对传播暴露和输入性感染数量进行知情估计。结果表明，大多数旅行带来的寄生虫输入风险相对较低，但可以识别出前往高传播地区并长时间逗留的风险群体。
匿名移动电话记录为数据稀疏地区的人类活动模式提供了有价值的信息。从桑给巴尔到坦桑尼亚大陆的人类移动模式估计表明，来自该人群的输入性疟疾风险分布不均；少数人是输入性疟疾的主要风险来源。与疟疾流行地区的空间数据和传播模型相结合，从电话记录中得出的活动模式可以说明疟疾输入的可能来源和输入率。这些信息对于评估消除疟疾的可行性和规划消除疟疾运动非常重要。
