Restaurants, gyms, cafes and other crowded indoor venues accounted for some 8 in 10 new infections in the early months of the U.S. coronavirus epidemic, according to a new analysis that could help officials around the world now considering curfews, partial lockdowns and other measures in response to renewed outbreaks.

The study, which used cellphone mobility data from 10 U.S. cities from March to May, also provides an explanation for why many low-income neighborhoods were hardest hit. The public venues in those communities were more crowded than in more affluent ones, and residents were more mobile on average, likely because of work demands, the authors said in the research published in the journal Nature on Tuesday.