Millions of cellphone users in Kenya are helping the fight against malaria. In the Oct. 12 issue of the journal Science, scientists report using cellphone location data to create a map of "sources" and "sinks" of malaria, which could lead to better-focused efforts against the mosquitoes that carry it.
The researchers used location data from every call and text made by a mobile phone user in Kenya -- 14.8 million of them. The location data was gathered from the 11,920 cell towers that dot the country, spread among 692 settlements. That data was used to track where people traveled. The researchers then superimposed maps of population density and the rate of infection of malaria. The prevalence of the number of people infected with the disease combined with the travel data was then used to establish a per-day probability that a person would be infected if they visited a specific location.
Malaria is caused by a parasite transmitted by mosquitoes, which bite an infected person and transmit the disease to someone else. In 2011, the disease resulted in some 655,000 deaths, 91 percent of them in Africa, according to the World Health Organization's 2011 World Malaria Report.
"We really got to work out where the infections are coming from," Caroline Buckee, assistant professor of epidemiology at the Harvard School of Public Health and senior author of the study, told Discovery News.
The combination of two "big data" sources enabled the research team to see travel patterns and use that to find areas where most malaria infections come from. "One of the 'great' things about malaria is that we have very high spatial resolution maps of prevalence," Buckee said. The map of prevalence can be broken up into areas as small as a kilometer (about a thousand yards) on a side.
Some people don't show symptoms immediately, so they can be carriers. That means draining a swamp or spraying a certain area might kill the local bugs, but if people carry the parasite from an area that is untreated, the eradication effort won't do any good.
The study found that many people travel from Nairobi to areas near Lake Victoria, where mosquitoes and malaria are prevalent. If infected, those travelers bring malaria back to Nairobi when they return. This is why there are more malaria cases showing up in Nairobi's clinics and hospitals than one would expect from the fact that there aren't many places for mosquitoes (of the species that transmits malaria) to live.
Buckee noted that the study doesn't involve finding someone with malaria and tracking their movements. Rather, it uses the data that local officials have about malaria prevalence and population density and combines it with the location information from the phone companies. That's combined with mathematical models of malaria transmission. There's no information about individual people.
Aside for malaria, Buckee said there has been interest from other researchers in applying this method to studies of dengue, another mosquito-borne disease that tends to show up in tropical countries. Dengue, in fact, might be even easier to study as it tends to show up in urban areas where there are more cell phone towers, and thus better data on human movement.