Cell phones are the latest tool epidemiologists have for fighting infectious diseases.

The novel technique—dubbed digital epidemiology—takes center stage in a new study published today in Science which tracks 15 million Kenyans with cell phone data to determine how population movement patterns influence the spread of malaria. The study was done by researchers at eight institutions including the Harvard School of Public Health.

“Every time someone uses their phone to call or text, we have an approximate location of that person and we can build up a picture of how they are travelling over time. Combining that data with a malaria prevalence map we can calculate a kind of movement map for malaria,” said Caroline Buckee, one of the paper’s authors.

Buckee, who is an HSPH assistant professor of epidemiology, explains the value of studying malaria.

“Malaria is a preventable and treatable disease but it kills 1 million people, mostly children, a year. It’s a global threat. It’s important to me that we try to solve this problem.”

She said that the focus of this study—the geographic spread of the disease—is crucial for understanding the transmission of malaria as a whole. According to Buckee, this study shows that traditional approaches to malaria control, which involve focusing on reducing disease in particular areas, are not sufficient.  Instead, it is important to study how malaria travels through areas.

“When people travel to areas with mosquitoes, they can become infected and bring back malaria to others. This undermines control programs. [Our study identifies] the high-risk areas for malaria parasites,” Buckee said.

One of these high-risk areas is Kenya’s Lake Victoria region. The research showed that there is a large eastward migration of malaria from this region to the nation’s capital Nairobi.

According to Buckee, Kenya was chosen as the subject of this study because its level of malaria prevalence is very geographically varied, it has excellent data on the disease’s spread, and nearly all Kenyans have cell phones.

Buckee also has similar projects in other parts of sub-Saharan Africa, and there is a growing interest in using similar methodologies to track mobility in the developed world.

“There’s a lot of interest in tracking people,” said Buckee. “It has definite applications to questions about healthcare and infrastructure. You can study how people respond to natural disasters. In Haiti they used this method to figure out how people were moving around after earthquake.”