About 220 passengers aboard the Norwegian Cruise Lines ship, Pride of Hawaii, fell ill because of a highly contagious Norwalk virus. The norovirus caused stomach flu, nausea, vomiting and diarrhea in passengers after they returned Monday to Honolulu following a seven-day cruise around the islands.

Janice Okubo, spokeswoman for the Hawaii Department of Health said, "It's one of the common viruses we've been seeing on cruise lines. Most of the time, people recover

Researchers have found one in every ten imported oysters screened in Hong Kong showed signs of norovirus, the term for the Norwalk-like virus that causes severe diarrhea and vomiting.

Senior investigator Dr. Wilina W. L. Lim notes outbreaks of gastric illness caused by norovirus are often linked to eating tainted oysters, making contamination fairly widespread