The stocks of American Airlines and several cruise lines were among the worst performers in the Standard & Poor’s 500 index Monday, as investors fret that the new coronavirus could take hold outside China and further disrupt international travel. Fears about the new virus’ effect on the global economy grew after a spike in new cases reported in Italy, South Korea and Iran.

Shares of Norwegian Cruise Line Holdings Ltd., Carnival Corp. and Royal Caribbean Cruises Ltd. tumbled about 9%. American Airlines Group Inc. shed 8.5%, and Delta Air Lines Inc. and online travel agency Expedia Group Inc. fell more than 6%.

CFRA Research lowered its investment rating on United Airlines Holdings Inc. to “hold” from “buy.” The firm says United is even more dependent on international revenue than American or Delta. However, United’s stock ended down a relatively modest 3.3%.

United investors might have been partially mollified by unrelated news that the airline extended a credit card agreement with Chase and Visa through 2029, increasing the deal’s 2020 cash contribution to the airline by an estimated $400 million. The extension was announced after the market closed Friday.

There are signs that the impact on travel in China, where the virus started, may be hitting a plateau or even easing. OAG, an aviation-data firm, said Chinese airlines scheduled an increase of more than 25% in seats on domestic flights this week, the first gain in more than a month.

However, OAG cautioned that the capacity increases could be “smoke and mirrors” – that Chinese airlines could cancel flights at the last moment. “Monitoring the actual number of flights operated in China this week will be interesting,” the firm said in a report.

China is the world’s second-biggest air-travel market. In the last six weeks, Chinese airlines have cancelled nearly the number of seats that airlines offer between the United States and Western Europe during an entire year, OAG said.