Spread of Zika linked to how much time people spend outside

Zika virus -- carried by Aedes mosquitos in select tropical and subtropical regions of the world -- is often transmitted indoors in developing countries. But in the United States, the majority of mosquito bites occur outdoors. Therefore, local patterns of how people spend their time outdoors are likely to contribute to how mosquito-borne viruses, including Zika, are spread.

In the new work, Marco Ajelli, of the Northeastern University, and colleagues of the University of Miami surveyed 270 residents of Miami-Dade County Florida about their time spent outdoors, and analyzed both the survey and previously published national data on outdoors time. Then, they used computational modeling to determine how Zika transmission dynamics related to time spent outdoors by people.

The researchers found that the amount of time spent outdoors by people in Miami-Dade County was highly variable; most people spent little time outdoors -- less than two hours a day -- but a small percentage of people spent a large amount of time outdoors. Their modeling then revealed that this heterogeneity -- compared to a hypothetical population in which everyone spent the same, average amount of time outside -- leads Zika virus to infect fewer people, but spread at a faster pace between people.

"This highlights the need to derive new indices to be considered by operational mosquito control programs, categorizing neighborhoods on the basis of both mosquito surveillance counts and human outdoor exposure risk," the researchers say. "Operation control efforts could be prioritized and directed toward areas characterized by high levels of human outdoor activities, such as recreational areas and tourist attractions, rather than, for instance, on residential areas."