SAN FRANCISCO – By the time the coronavirus-stricken Grand Princess glided across this city’s fabled bay Monday, the massive cruise ship had galvanized the world’s attention.

That dramatic scene may well have multiple sequels: Dozens of cruise ships are poised to hit U.S. cities as some port authorities, including those in Monterey and Santa Barbara, close their docks to large passenger ships. All embarked well before cruise lines started cancelling future cruises last week.

At least 30 cruise ships at sea list port destinations in the USA this week, according to a USA TODAY satellite tracking analysis of 380 of the world’s largest cruise ships. Data from real-time vessel monitoring systems was merged with passenger and crew capacities to produce the snapshot.

That means upward of 100,000 people – 70% of them passengers – could look to come ashore at a range of U.S. ports, based on the average capacity of the ships from cruisemapper.com. Since this is prime Caribbean cruising season, more than a dozen of those 30 ships are bound for the Florida cities of Key West, Cape Canaveral, Fort Lauderdale and Miami. Next up: the Alaskan season, due to start in early April, with stops in Seattle and Juneau.

Cruises by their very nature pour people, and money, into economies across major coastal U.S. cities, so barring them is a decision not taken lightly by officials.

“At this point, we’re not planning to close the port of Juneau, but we’ll keep watching this quickly evolving situation as the impact grows,” says Mila Cosgrove of the City & Borough of Juneau, which controls some of the docks in an Alaskan Inside Passage cruise hub that hopes to welcome 1.5 million visitors this summer. “We wouldn’t close without the belief that either health or public safety is in jeopardy.”

As the coronavirus raced across the nation in the past two weeks, at least 104 of the 360 ships tracked by USA TODAY stopped at U.S. ports. Those ships in total can carry up to 280,000 passengers and 113,000 crew.

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The world’s largest cruise ship, Royal Caribbean’s Symphony of the Seas, left Miami last weekend for a Caribbean cruise and is scheduled to head back there Saturday with a staggering capacity of 5,000 passengers and 2,300 crew.

None of the ships at sea has reported passengers with symptoms of the coronavirus, or COVID-19. Such a report could, as was the case with the Grand Princess, trigger changed itineraries, port delays, helicopter evacuations and long quarantines.

For some cruisers, those prospects are enough to scuttle plans.

“It was less about the virus and more about the impact of a possible quarantine,” says Mark Eickhoff of Lansdale, Pennsylvania, who was due to join the Symphony of the Seas cruise around the Caribbean this week. “You have 5,000 people on the boat, but one person gets sick, and everyone is impacted. That’s too high-risk for us.”

Aside from the Grand Princess, the three other large cruise ships with recent cases of the coronavirus are the Diamond Princess, the World Dream and the Westerdam. The MS River Anuket, a Nile River ship, also had a confirmed case.

$45B cruise industry in virus’ sights

Experts say there is palpable concern as the $45 billion cruise industry powers ahead despite advisories from the State Department and Centers for Disease Control and Prevention that discourage cruise travel, as well as long airplane journeys.

The leading cruise trade organization sent a proposal to the White House suggesting a new policy to deny anyone older than 70 from boarding without a doctor's note verifying their fitness for travel. The proposal by the Cruise Lines International Association would also bar anyone with chronic medical conditions.

“This is our busy winter season, so everything moves ahead now but on a case-by-case basis,” says former Coast Guard officer Corey Ranslem, CEO of the Fort Lauderdale-based International Maritime Security Association, a consultant for large vessel operators.

“All cruise lines are screening crew, but it’s more difficult with passengers,” Ranslem says, noting these ships are giant floating hotels holding 3,000 people that get turned over each week. “It’s all the new normal I guess, but everyone is being very careful.”

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After a meeting Monday with Vice President Mike Pence – who oversees the White House effort to combat COVID-19 – Kelly Craighead, president of the Cruise Lines International Association, had lamented the State Department cruise warning and said her industry works hard to protect passengers and crew.

“We are moving forward and remain focused on development of an aggressive, responsive plan,” Craighead said in a statement. “Our first priority is to protect our guests, our crew and the communities where we sail.”

At least one cruiser has been impressed with new dockside measures. Paul Whiting from just north of Oxford, England, is on the Symphony of the Seas. Before embarking, passengers had their temperatures checked, and some were turned away.

“We aren’t overly concerned right now but are monitoring all ongoing information,” Whiting says, adding that the ship has lots of hand sanitizer and rooms set aside for quarantine and the crew makes frequent announcements about washing hands in multiple languages.

“To be honest, I was more concerned about the flight and the number of people onboard for over nine hours,” he said.

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Cruise ships underway are due to make their scheduled stops against a backdrop of mounting alarm over the spread of COVID-19. After breaking out of China late in 2019, the virus has resulted in more than 125,000 cases and more than 4,500 deaths worldwide.

The crisis caused beleaguered Italian lawmakers to enact no-travel measures and generated calls for extreme social distancing in the USA, where more than 1,000 have tested positive across 37 states. At least 32 people have died in the USA, leading to fears that the highly contagious virus is far more lethal than the flu.

Cruise ships in the virus spotlight

Cruise ships have come under particular scrutiny because their close quarters provide a perfect petri dish environment for a virus.

The Diamond Princess was docked in Yokohama, Japan, for two weeks after a COVID-19 outbreak in early February. Out of the 3,700 total passengers, 619 were infected, a rate about eight times higher than if passengers had been allowed to disembark, researchers found.

Once the Grand Princess finally arrived in Oakland on Monday, passengers – only two were infected, in addition to 19 crew, at the time of docking – were whisked off to quarantine facilities at military bases across the country.

The prospect of potential virus carriers unknowingly wandering port cities worries civic leaders.

Announcements by city managers in the California cities of Monterey and Santa Barbara stressed that public health concerns led them to ask cruise lines to bypass those port hubs until federal cruise advisories are lifted.

Canadian officials are mulling a similar decision. Bonnie Henry, the top health official in British Columbia, said this week that officials “should be delaying our cruise season until we are in a safer place internationally.”

That could be devastating to cruise ships sailing to Alaska, for a technical reason.

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Most cruise ships do not fly U.S. flags in part because doing so means hiring American workers at wages higher than those paid to foreign workers, many of whom are from Southeast Asia. Ships flying a non-U.S. flag must stop at a foreign port between U.S. stops, such as Mexico or Canada. If Canada is no longer a port option, ships effectively can’t get to Alaska from the USA without the standard stop in Vancouver.

At the Port of Seattle, there’s a wait-and-see attitude, spokesman Peter McGraw says.

“We’re reviewing multiple options about the launch of the cruise season,” he says. “It’s a valuable part of our local economy, and we want to be deliberate about any decisions.”

The season was due to kick off April 1 when passengers were to board the Grand Princess after it received the necessary cleaning and official clearance for sailing.

Who can block a ship from port?

The question of who controls access to a U.S. port is at once simple and complex.

USA TODAY reached out to governors’ offices in nine port-city states: Florida, California, Louisiana, Washington, Maryland, Texas, New York, Alaska and Hawaii. The few offices that responded confirmed that jurisdiction over docking privileges involves, to varying degrees, city officials, the CDC and mainly the Coast Guard.

“Similar to airports where the FAA operates the air traffic control tower, the U.S. Coast Guard is the Captain of the Port, or COTP, which controls when and where vessels enter a commercial harbor,” Jodi Leong of the Hawaii governor’s office wrote in an email. “The State of Hawaii does not have jurisdictional authority to ban cruise ships from coming to port in Hawaii.”

The Coast Guard works in conjunction with myriad officials, including the CDC, Customs and Border Protection and port officials, to “assess situations on a case-by-case basis,” says Coast Guard spokesman Barry Lane. “If necessary, the Coast Guard can issue a COTP order to restrict a vessel’s movement.”

Even if the Coast Guard granted a ship clearance – after the ship showed it did not pose a health risk or danger to the port city – local officials in theory could block its arrival simply by not making the dock available, like welcoming a car into a parking lot with no open spaces.

Though the almost daily changes in the COVID-19 outbreak could radically alter plans for cruise ships around the country, the past two weeks showed no letup of cruisers hitting top U.S. ports.

USA TODAY’s analysis shows Miami was the busiest of these cities, with at least 21 cruise ship stops in recent weeks, followed by Cape Canaveral with 14 and three cities with 12 stops each: Key West, Port Everglades and San Juan, Puerto Rico.

This traffic puts pressure on officials in those cities to make what could be unpopular decisions.

Coronavirus not stopping some

For some travelers, the lure of the seas remains more powerful than the fear of COVID-19.

Jacob Sigo of Vancouver, Washington, is aboard the Norwegian Joy for a seven-day Mexican Riviera cruise. In port at Cabo San Lucas on Tuesday, Sigo told USA TODAY that he was apprehensive about the trip but went anyway because he felt healthy and couldn’t cancel flights without a penalty.

He was prepared to self-quarantine and work remotely upon his return if necessary, he said.

Once Sigo got on board, things seemed oddly unaffected by the virus news. That quickly changed, showing that cruise lines are still adapting.

“We were among the first to board the ship, and I was really surprised to see the entire buffet area open for self-service, including beverage stations,” he said. “By day two, the buffet areas were cordoned off, and all the utensils turned inward, so staff could serve the food.”

Whether such measures are enough to reassure not only passengers but also a growing number of port city officials concerned about citizens in their community remains to be seen.

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Kristen Fowler of Brentwood, Tennessee, isn’t taking any chances. She struggled for a week to scrap her trip with other moms and their graduating high school seniors aboard the Regal Princess, which is set to leave Sunday for the Caribbean.

That same ship was held up off the Florida coast last week awaiting COVID-19 test results on two crew members who previously had been aboard the Grand Princess. When they turned up negative, passengers disembarked, and the ship was readied for its next journey – one Fowler was supposed to join.

“My main concern isn’t catching coronavirus, it’s being stuck on a ship that can’t port anywhere and then being quarantined after that,” says Fowler, who spent four hours on hold with Costco to cancel her trip. “An update today says they are cleared to start cruising, which is incredibly irresponsible to me.”

USA TODAY investigative reporter Nick Penzenstadler (@npenzenstadler) reported from Wisconsin; national correspondent Marco della Cava (@marcodellacava) reported from San Francisco.