(CNN) — The State Department is urging Americans not to board cruise ships as coronavirus cases rise across the US.
The warning is particularly for people with underlying health conditions, the State Department said in an advisory on Sunday.
Underlying conditions include heart disease, chronic lung disease, diabetes and conditions that suppress the immune system, the US Centers for Disease Control and Prevention said in separate guidance recommending that people with such conditions "defer all cruise ship travel worldwide." The CDC said it usually advises against destinations -- not transportation -- during outbreaks, but that the novel coronavirus is an exception.
"Recent reports of COVID-19 on cruise ships highlight the risk of infection to cruise ship passengers and crew. Like many other viruses, COVID-19 appears to spread more easily between people in close quarters aboard ships," the CDC said.
There are now 34 states with cases of the virus, bringing the national total to 565. That number includes 46 people who were former passengers of the Diamond Princess cruise ship and at least 21 people who tested positive for the virus while aboard the Grand Princess cruise ship, which will dock in California Monday.
In response to the outbreaks, Princess Cruises, which operates both ships, is offering stranded passengers aboard the Grand Princess cruise ship a full refund, according to a letter obtained by CNN. The refund includes air fair and accommodations as well as a future cruise credit.
A top US health official also warned against cruise ship travel for older adults with underlying health conditions.
"We want people who are older, people who have medical conditions, to take steps to protect themselves, including avoiding crowded spaces, including thinking very carefully about whether or not now is the time to get on that cruise ship, whether now is the time to take that long haul flight. For most people you're going to be fine. But if you have medical conditions, or you're older, now is the time to rethink that," Surgeon General Dr. Jerome Adams told CNN's "State of the Union."
CNN has reached out to the cruise industry trade association for comment.
Cruise Lines International Association said in a tweet Friday, before the State Department's advisory, that restricting cruise ship travel is "unwarranted" and contradicts the World Health Organization's stance against travel or trade restrictions to countries experiencing an outbreak of the novel coronavirus.
Meantime, in Puerto Rico, where there has yet to be a confirmed case of coronavirus, a policy now mandates that cruise ships attempting to enter Puerto Rico must first validate that there are not cases of coronavirus on board, Gov. Wanda Vazquez Garced tweeted.