How can you predict the spread of malaria in a region like Zanzibar, where few records are available showing how people travel from place to place?

US researchers have found a novel answer to that question: How about by studying mobile phone records instead?

As part of a study commissioned by the Zanzibar government, a research team at the University of Florida obtained records of three months of calls — more than 21 million in all — from customers of the Zanzibar Telephone Company, which covers all of Tanzania and Zanzibar, a semi-autonomous region of Tanzania. The records contained no names or other identifying information, but enabled the team to track the movements of 770,369 customers by showing each customer’s calls and the region where those calls originated.

By analysing those records, the researchers found that most residents who leave the region make short trips to Dar es Salaam on the Tanzanian mainland nearby, where malaria is relatively uncommon. However, the team also found that a few Zanzibar residents travel back and forth from more distant areas of Tanzania where the risk of getting the disease is much higher.

The Zanzibar government’s concern is that people who visit high-risk areas will be bitten by mosquitoes carrying the disease, then return home where other mosquitoes can bite them and then transmit the disease to others.

“That group of the population is the real risk if Zanzibar wants to eliminate malaria,” said Andy Tatem, an assistant professor of geography and lead author of the study likely to appear in the January issue of the Malaria Journal. “That is the population group that is likely to be continually reintroducing infection.”

Zanzibar has drastically reduced malaria in recent years, and its government is now considering whether to launch a total elimination campaign.

Tatem said the study gives Zanzibar’s government several options should it move forward with elimination. The government could choose to give residents prophylactics against malaria before they travel, or it could screen all residents as they return, both of which are expensive propositions. Or it could launch a targeted information and/or screening campaign aimed at the high-risk travelers.

Zanzibar will use the study in combination with another study — of the challenges and costs of eliminating the remaining infections within the country — to make its decision.

“Going for elimination can be very expensive, much more expensive than continuing with current sustained control, involving giving people bed nets (to protect against mosquito bites at night), spraying the inside of houses with insecticide and providing anti-malarial drugs,” Tatem said. “But in the very long term the savings (of) having no malaria may outweigh those costs.”

• World Malaria Day kicks off disease-fighting campaign