The Centers for Disease Control said on Sunday that 172 people on a cruise ship arriving in California had fallen ill with the highly contagious norovirus during a nearly month-long trip.
The Crown Princess has more than 4,100 people on board; it was scheduled to be met by CDC staff upon arrival in San Pedro. CDC staff will conduct testing and evaluate the response.
In April, 129 people on the same ship contracted norovirus during a seven-day cruise off the California coast.
Princess Cruises did not immediately provide comment.
The CDC said the cruise line was consulting with it to ensure the ship was sanitised and disinfected before it was used for another trip on Sunday.
Norovirus symptoms include vomiting, diarrhoea, fever and body aches. The CDC says most people recover within three days.