The new coronavirus has struck hardest in working-class neighborhoods in New York City’s outer boroughs, city data shows, underlining how the pandemic has ravaged densely packed lower-income areas where social-distancing guidelines have proved difficult to implement.

Two areas of Queens—Corona and Elmhurst—have led the city in reported infections, with 947 and 831 as of March 31, respectively, the data show. Both neighborhoods are heavily populated by immigrants who live in close quarters, often with multiple families sharing a dwelling, said City Councilman Francisco Moya.

Many residents there don’t have the luxury to telecommute because they work in the hospitality industry, at restaurants or supermarkets, he said. “One person gets sick, it spreads around that household,” said Mr. Moya who represents Corona.

New York City has become the U.S. epicenter of the coronavirus pandemic and the Covid-19 disease that the pathogen causes. As of Wednesday morning, there were 44,915 positive cases in the city and 1,139 deaths. Queens had the most positive cases, with 14,966, and the most deaths in a borough, with 386.

Dr. Mitchell Katz, the chief executive and president of NYC Health + Hospitals, said it is difficult for some people to isolate and maintain social distancing to slow the spread of the virus, especially in the hardest-hit neighborhoods in Queens. “You may have multiple families living together in a very small apartment, so it’s easy to understand why there’s a lot of transmission of Covid occurring,” he said Wednesday.