WASHINGTON — The U.S. services sector, where most Americans work, grew for a fourth straight month in September as the country continued to reopen following a spring shutdown.

The Institute for Supply Management reported today that its index of services activity rose to a reading of 57.8 last month, 0.9 percentage point higher than the August reading of 56.9. Any reading above 50 signifies expansion in services industries such as restaurants, department stores and delivery companies.

The index had fallen sharply for three months starting in March as shutdowns aimed at containing the virus closed many businesses and put millions of Americans out of work. But starting in June, the index resumed rising and now stands above its February level of 57.3.