Vast amounts of mobile phone data have been used to build a picture of how the trips people make within Kenya might contribute to malaria transmission.
The researchers from Harvard School of Public Health worked with Oxford University researchers based in Kenya at the KEMRI-Wellcome Trust Research Program and colleagues from six other institutions.
They combined cell phone data from almost 15 million people in Kenya with detailed information on the regional incidence of malaria, providing maps of how human travel patterns contribute to the disease's spread. The findings are published in the journal Science.
Oxford University's Professor Bob Snow, who is based in Nairobi, says: 'People frequently move short and long distances for work and family. We don't really know very much about how people move and why they move, and what they contribute to infectious disease transmission in Africa.
'Having no data is a perennial problem in disease epidemiology on the continent and often we need to use our imaginations on how we might construct data. Africa leads the revolution in cell phone expansion, and the paper is a good example of how we might exploit this technology to work out where people move from and to.'
The researchers led by Dr Caroline Buckee of Harvard School of Public Health found that a surprisingly large fraction of 'imported' infections – that is, infections that are carried by people moving from one place to another – wind up in Nairobi, with infected residents returning there after journeys to spots such as Lake Victoria.
Professor Snow explains that the KEMRI-Oxford-Wellcome programme has been working for over 20 years to help the Kenyan government understand the epidemiology of malaria, and how best to use this information to guide decisions on malaria control. This has included producing maps of malaria risk for the government.
He says: 'We saw this collaboration with colleagues in Harvard as a
novel way to adapt what we know about malaria risk with what they could
squeeze from terabytes of data on cell phone use to ask what risks are
posed by people moving from high transmission areas to currently low
transmission areas, and vice versa.'
Malaria transmission in many, but not all parts of Africa is declining. 'On the Kenyan coast malaria transmission has dropped like a stone in last 10 years, largely due to scaled malaria intervention,' says Professor Snow. 'Mosquitoes still live there but parasites in the human population have declined. That's not so around Lake Victoria where transmission is still high.'
He explains that knowing the connections of people who live on the coast with the lakeside region through travel, and those who live there with the coast, might provide a measure of the risks of malaria importation.
'What the paper shows is that the country is so connected by travel that it is probably impossible to think of malaria elimination on the coast. We're all connected,' says Professor Snow. 'This has value when in dialogue with ministers who feel that we can do things sub-nationally.'
He adds: 'A practical but not directly related consequence of the work is that it would be possible to set up an automated alert through cell phone towers to people who have their phones registered in low transmission areas and make their first call in a high transmission area – "You are now in a high risk area - if you develop fever get checked for malaria immediately."'