The use of mobile phone data for the estimation of the travel patterns and imported Plasmodium falciparum rates among Zanzibar residents

Abstract

BackgroundMalaria 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 compromizing 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.Data and MethodsRecords 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.ResultsOver 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.ConclusionAnonymous 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 fo...

International population movements and regional Plasmodium falciparum malaria elimination strategies

“…Thus, though these analyses present a starting point and evidence base for the analysis of global and regional patterns of the relative levels of parasite movements between countries, they certainly provide no replacement for detailed assessments of human movement patterns, and should not be interpreted beyond relative measures of regional movements. In the new era of elimination it will be important to understand the forces that govern parasite migration, and a wide range of datasets, techniques, and tools now exist for quantifying human movement patterns across a range of spatial and temporal scales (30)(31)(32)(33)(34), and ultimately provide validation for some of the assumptions made here. Moreover, modeling frameworks are being developed in an effort to aid understanding the effects of movement upon transmission (34,35).…”

“…A global analysis of likely malaria infection movements should ideally be based upon subnational data on population flows, capturing the full range of relevant movements (30,34,36). However, such data are nonexistent for the vast majority of countries (particularly malaria-endemic countries), and both patchy and extremely variable for the remainder of countries, even highly developed countries.…”

Dynamic population mapping using mobile phone data

“…Most of these studies focused on specific cities or city neighborhoods or groups, and were aimed at understanding traffic flows (40), mapping the intensity of human activities at different times (42)(43)(44), or exploring seasonality in foreign tourist numbers and destinations (45,46). Population movement analyses based on MP data are particularly promising for improving responses to disasters (47,48) and for planning malaria elimination strategies (49)(50)(51). However, to date, these data have not been assessed in their capacity to map human population at fine spatial and temporal resolutions over large geographical extents.…”

Special issue on global health

“…As well as directly improving access to information about health and healthcare for everybody, this will also improve the availability of data for research and analysis (see e.g. [12]). -Deepening Research Capacity.…”