U.S. stocks fell Wednesday as pockets of coronavirus infections emerged in several states, adding to concerns about a second wave of cases that could lead to renewed restrictions on business activity.

The Dow Jones Industrial Average fell 237 points, or 0.9%, to 25917 shortly after the opening bell. The S&P 500 declined 0.7%, and the Nasdaq Composite lost 0.3%.

New coronavirus cases have jumped in several states, with Arizona, Texas and California reporting daily records of infections Tuesday. Texas Gov. Greg Abbott and Florida Gov. Ron DeSantis said they would step up enforcement of social-distancing guidelines. California Gov. Gavin Newsom said earlier this week that the surge in cases could force the state to implement stricter measures on businesses and social gatherings once again.

“If this does get worse and more endemic, they will have to lock down some of these states again,” said Charles Hepworth, an investment director at GAM Holding. That could lead to another drop off in economic activity, threatening the stock market’s nascent recovery.

Carnival shares lost 5.1% Wednesday after S&P downgraded the company’s credit rating, saying the cruise industry faced a long period of weak demand. Shares of other cruise operators also declined, with Norwegian Cruise Line falling 5.3%.

Investors’ concerns about the rise in infections have in recent weeks been tempered by optimism about stimulus measures from central banks and major governments, reflected in the rally in most major stock markets.