The team "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 or the coast," the news release says.
This may lead to an increased risk of local transmission within Nairobi and its surrounding areas, despite the lower number of mosquitoes, or "malaria vectors," in urban areas.
The research suggests that efforts to control malaria could benefit from a focus on "source" areas where incidence is high, rather than on areas where fewer people are infected. Human travel patterns mean the parasite is likely repeatedly to be carried back to areas where it has been almost eliminated.
The study advises that on a very local scale, "hot spots of transmission can be targeted by indoor residual spraying, vector habitat removal, insecticides, drug administration, and bed-net use."
But attempts to control transmission by targeting human travel between regions "will be completely different from those that concentrate on local transmission hot spots, focusing on communicating risks to travelers to alter their behaviors, restricting travel patterns, and/or conducting routine surveillance in high-risk areas."
This could mean encouraging people from areas of high prevalence to use insecticide-treated bed nets when traveling to areas of lower malaria incidence to avoid bringing the parasite with them.
It also advises visitors to areas such as Lake Victoria to take greater care not to become infected before their return home.
Wesolowski acknowledges certain limitations such as following only cell phone users in areas where there are cell towers and inability to track people's cross-border movements.
However, the importance of such research into one of the world's largest preventable causes of death should not be underestimated.
There were about 216 million cases of malaria worldwide in 2010 and about 655,000 deaths from the disease that year, according to the World Health Organization.