Clark County Health District officials said a Norwalk virus — which has symptoms of vomiting and diarrhea like a stomach flu — infected at least 100 guests of the downtown Las Vegas hotel. But environmental health supervisor Daniel Maxson said no cause has been pinpointed at the hotel or the Omni Air airplane that took the guests to Nevada.

"There’s an association with that hotel," Maxson said. "Precisely how it is being transmitted, we don’t know." Maxson said health officials ruled out the restaurants — which all received the highest grade A rating in the latest inspections.

Since November, Maxson said Las Vegas saw a community spike in gastroenteritis or stomach flu-like illnesses.

Maxson said he expects more people may report illnesses after seeing news stories about the virus outbreak.

He said the hotel has passed on any reports of illness that it has received and has stepped up its cleaning procedures and suggesting preventive handwashing for visitors and employees.

Maxson reminds all visitors to wash their hands after using the restroom and before they eat, which people may forget when they are on holiday. "You might touch a casino’s desk of cards, touch a slot machine that others have touched," he said. "If you don’t go wash your hands before you eat, you might get sick."

Rob Stillwell, spokesman for hotel owner Boyd Gaming Corp., said the hotel is cleaning more frequently and asking guests and employees to wash their hands more frequently. Even though health officials have found no cause of the disease on their property, "we stepped up our efforts," he said, "just being extra careful."

The California Hotel remains a popular island getaway destination for many Hawai'i residents.