By the time major cruise lines halted new voyages last Friday, at least half a dozen other ships had sailed with at least one passenger later diagnosed with the highly contagious virus.

While cruise lines have seen only a small fraction of the pandemic, they have emerged as a particularly tricky battleground to fight the virus. Health experts said the industry’s initial resistance to take drastic action — coupled with a deference from government officials, who let the companies come up with their own action plan — put more passengers at risk.

“The cruise ship response was definitely lagging behind expert opinion on how big the risks are,” said University of Chicago epidemiologist Katelyn Gostic. “It was sluggish decision-making, and they should have responded earlier.”

The crisis has put the spotlight on an industry that critics say for years has skirted labor regulations, such as minimum wage, and federal income taxes by incorporating overseas. Yet when disasters strike, or when people get sick or fall overboard, federal agencies such as the U.S. Coast Guard come to the rescue.