Health officials turn to mobile-phone data to track Ebola spread in Congo

Health officials ​battling the Ebola outbreak in eastern Democratic Republic of Congo are using anonymised mobile-phone data ‌to ​map population movements and identify areas where the virus could spread next, according to the World Health Organisation and researchers working with it.

The approach, which has not been used before in an Ebola response, comes as authorities struggle to contain what the WHO has described as the fastest-growing Ebola outbreak on record. Cases have been confirmed in six provinces, with more than 6,250 people ‌infected and 3,039 killed since the outbreak was declared on May 15, according to the latest government data. The outbreak, Congo's 17th, is caused by the Bundibugyo species of Ebola, for which there are no approved vaccines or treatments.

IDENTIFYING AREAS AT RISK As the virus spreads, health officials are looking for ways to anticipate where cases could emerge next and direct limited surveillance and response resources.

"Population movements have always been a factor in outbreaks, but they are particularly important in the current epidemic," said Olivier Le Polain, head of epidemiology and analytics for ‌response at the WHO Health Emergencies Programme. Traditional risk assessments focus on outbreak hotspots and assume the virus is most likely to spread to surrounding areas. Analysing mobility data allows responders to identify risks in places that may be geographically distant but ‌closely connected through travel patterns.

"It gives us a more nuanced understanding of risk," Le Polain said, citing the example of Ituri province, in the northeast, where the virus is believed to have started circulating. "There are very significant population movements in Ituri linked to mining activities and trade. Understanding those movements is crucial to understanding how the outbreak spreads."

The analysis is produced by Swedish non-profit Flowminder, using anonymised records generated when mobile phone users connect to telecommunications networks. As people move around the country, their phones connect to different antennas on the network, generating records that show where those connections took place. Researchers use those records to estimate how people travel ⁠between different areas. The ​data is provided free of charge by Vodacom, Congo's largest operator. Vodacom ⁠did not respond to a request for comment.

Flowminder says it receives aggregated and anonymised records and does not have access to information identifying individual subscribers. "We seek to provide estimates of how people move, which in turn is a predictor of how infectious people move," Flowminder founder Linus Bengtsson told Reuters.

Flowminder's first analysis, published ⁠in early June, focused on the three areas where the outbreak is believed to have started: Bunia, Mongbwalu and Rwampara. Researchers tracked where people who had spent time in those areas between April 3 and April 23 later travelled. The largest flows were to nearby areas in Ituri province and North ​Kivu province. By the end of June, all 10 of the destinations receiving the largest flows of travellers from the original outbreak areas had reported confirmed Ebola cases.

SUPPORTING THE RESPONSE As the virus spread beyond its initial epicentre, ⁠Flowminder expanded the analysis to additional affected areas, examining where people leaving those hotspots were most likely to travel.

One location that drew particular attention was Kisangani, a major transport hub on the Congo River that connects eastern and western Congo. "The fact that Kisangani was at risk was not a huge surprise, even if it was not ⁠bordering ​the affected areas," Le Polain said. "By mid-June, the data showed the risk was significant and that the outbreak could spread there faster than we initially thought. We strengthened operations there before the first cases were detected."

More recent studies have highlighted links between Kisangani and Kinshasa, as well as settlements along the Congo River and areas near the borders with Central African Republic and South Sudan. Fifteen of the 50 areas most connected to Kisangani were in Kinshasa province, highlighting the potential risk of spread to Congo's capital and ⁠largest city. The findings come as the WHO continues to warn of the risk of the outbreak spreading to Kinshasa and neighbouring countries. In a modelling exercise presented in late June, the agency estimated there was a 70% probability of a case ⁠being detected there by the end of September.

COVERAGE GAPS One limitation is ⁠that the analysis relies on data from Congolese mobile-phone networks and therefore provides only a partial picture of movements across international borders.

It also currently relies on data from a single telecom operator in Congo, Vodacom. While the company is the country's largest operator, with more than 26 million active subscriptions and a market share of nearly 35%, the analysis cannot capture the movements of people ‌using rival networks. Flowminder and U.N. officials involved ‌in the response say efforts are under way to secure similar agreements with other operators to improve coverage and get more detailed ​data.