JACKSONVILLE, Fla. -- Almost 100 passengers on a five-day cruise aboard the Celebration out of Jacksonville last week reported stomach illness.

According to a statement by Carnival Cruise Lines, "an elevated number of incidences of gastrointestinal illness were reported to the ship's infirmary. While unconfirmed pending the outcome of test results, the instances of GI distress being reported are believed to be the result of a norovirus."

The illnesses were reported to the Centers for Disease Control and Prevention since 99 passengers reported symptoms, exceeding the 2 percent guidelines for CDC to consider it an outbreak.

Carnival says the ship was vigorously cleaned and disinfected after the Celebrity returning to port on Saturday, and no illness is reported during the ship's current cruise.

For all voyages during the peak winter norovirus period, Carnival said it provides passengers are given a letter with information on norovirus, its symptoms and tips for avoiding transmission.

The CDC estimates that 23 million people in the United States every year contract norovirus, or 8 percent of the U.S. population. Symptoms of norovirus typically last one to two days. The most common way of transmission is through person-to-person contact.

Although Carnival said that less than 1 percent of all cruise ship passengers are affected by norovirus, cruise lines encourage guests to practice washing hands frequently and thoroughly.

On The Net: CDC Information On Norovirus