Your cell phone location information can be used to help you find restaurants or help companies serve you targeted ads. What if all of this data could also play a role in studying and fighting deadly infectious diseases, such as malaria? An international team of researchers has done just that—for an entire country.
People can travel much farther, and far more quickly, than the mosquitoes that carry the malaria parasite (Plasmodium falciparum). The research team, led by Amy Wesolowski, of Carnegie Mellon University's Department of Engineering and Public Policy, was able to analyze cell phone location information for each of Kenya's 14.8 million cell phone users. Even phones without GPS are providing general location info based on what cell towers they are using. The research was published online October 11 in Science.
Each call and text that was fed through one of 11,920 cell towers logged that individual's location. People were ascribed a home area based on their most often used cell tower. Then each journey within the country could be tracked as cell phone users moved to different cell tower ranges. "Over time we can build up a picture of how they're traveling between towers on a weekly or monthly basis," study co-author Caroline Buckee of the Harvard School of Public Health explained in a Science/AAAS podcast interview.
A year's worth of this information (June 2008 to June 2009) was then merged with highly detailed maps of malaria prevalence and estimates of infection risk. "So we had a really enormous dataset," Buckee said. This massive amount of data allowed them to create detailed maps of travel to and from malaria hotspots—and to make predictions about how human travel has affected the transmission of the disease.
Many people who are infected with the parasite might not show symptoms or, at least, not show them right away. As a result, they could carry the parasite hundreds of kilometers to infect other mosquitoes—and potentially other humans—as they head toward their destinations.
"Malaria control programs must account for this human travel-mediated spread of parasites because frequent introduction of imported parasites could undermine local control or elimination strategies," wrote Buckee and her colleagues in their study.
The researchers found that many of the journeys, as mapped via cell phone data, involved travel to or through the capital city, Nairobi, where previous malaria eradication efforts and urbanization have pushed the illness to low levels and reduced the number of potential carrier mosquitoes. Thus, even the many visitors to the city who might be infected and city residents who have become infected while traveling to other regions are unlikely to cause a large spike in subsequent transmission of the disease there.
Many other areas of the country, however, are at higher risk from imported cases of malaria, according to the travel maps. Some of the most vulnerable places are those in the central and Lake Victoria region, which offer more potential vectors and less robust eradication progress. Those people moving within these regions, between areas where malaria has high and low prevalence, might actually be one of the biggest forces of spreading the illness.
"Mapping the routes of parasite dispersal by human carriers will allow for additional targeted control by identifying the regions where imported infections originate and where they may contribute substantially to transmission," the researchers wrote. With this information, governments could focus efforts on areas that were likely to both contribute and receive the highest number of infections. New control efforts could include boosting surveillance in these places, improving communication about risk of travel to these areas, and perhaps even sending text messages to travelers if they are visiting a high-risk region.
Each year, some 216 million people worldwide still get infected with malaria, according to the World Health Organization, and some 655,000 people die from the disease.