Tracking the Spread of Disease in Cities.

• Position: CONTAGION

Everyday travel within a city--especially commuting--is an important factor influencing the spread of certain diseases in urban settings, according to a study published in Nature Scientific Reports, which used aggregated mobile phone data to trace the spread of dengue, a mosquito-borne virus.

While many studies have linked human travel to the spread of disease over long distances, the current finding is notable for its granularity, tracking the path of contagion over shorter distances and times. Future research will be needed to determine whether the findings also apply to airborne diseases, such as the flu.

"Human mobility is an important factor in the vector-borne disease epidemics at the urban scales," says corresponding author Emanuele Massaro, a scientist with the Laboratory for Human-Environment Relations in Urban Systems at the Swiss Federal Institute of Technology. The new method, he notes, means that researchers looking at the issue on a city-wide basis "do not need very detailed tracking of individuals that could infringe on privacy, but [can still use] models that capture the key facet of mobility: commuting!"

To conduct the study, the researchers examined how different models of human movement fit with spread of dengue fever in Singapore during the outbreaks of 2013-14. Dengue fever is transmitted from mosquitoes to people; there are an estimated 50,000,000 human infections annually around the world, leading to about 500,000 hospitalizations and 25,000 deaths each year.

Given health data about the spread of dengue fever in Singapore, the researchers created four models of human mobility in the city-state during this time. The models used data about the estimated number of mosquitoes per human and the mosquito bite rate. The researchers then evaluated which model of mobility corresponded best with the propagation of the illness.

The first model used anonymized call records for 2,300,000 people in Singapore from 2011, showing a typical pattern of population movement; the second model, by contrast, assumed random movement; the third model used a common probability distribution to estimate everyday movement of people; and the fourth model used census data showing home locations, then applied a paradigm of urban movement previously developed by scholars (a "radiation model") to estimate travel in Singapore. The researchers then ran a series of simulations for each model.

Given the numbers of mosquitoes and the infection rates, the...