Health officials say cruise ship passengers are getting sick with a stomach bug less often.
About 20 outbreaks are reported each year on ships that dock at U.S. ports, on average. Many draw media coverage.
But it's becoming less common for passengers to get sick, according to figures released Thursday by the Centers for Disease Control and Prevention.
Since 1990, the illness rate has fallen from about 29 to 22 per 100,000 passengers. Officials say cruise ship companies are doing more to disinfect ships and prevent outbreaks.
It wasn't a steady decline. Cases spiked in 2012 when a new strain of norovirus emerged. Norovirus causes most stomach illnesses on cruise ships.
Related: Norovirus is Easy to Get, Hard to Get Rid Of
Norovirus makes 21 million people sick every year in the United States. Separately on Thursday, New York City education official said the virus sickened 210 students at a single public school in Queens this week.