The ship is currently carrying 138 people who have complained of flu-like symptoms, which are similar to coronavirus symptoms. Two people have tested positive for coronavirus.
"Our thoughts and prayers are with their families and we are doing everything we can to support them during this difficult time," Holland America Line said of the four who had died of undisclosed causes in a statement shared by spokesperson Erik Elvejord.
Elvejord added that Holland America Line couldn't share whether those passengers had reported coronavirus symptoms due to privacy regulations.
Those on the ship who are sick include 53 passengers and 85 crew members. There are 1,243 passengers and 586 crew members on the ship, including 305 Americans.
The ship did not have coronavirus tests available on board until Thursday evening when it rendezvoused with Holland America's MS Rotterdam for additional supplies and medical personnel. On board the Zaandam there are four doctors and four nurses, and the Rotterdam is carrying two doctors and four nurses, the cruise line said.
The two ships received permission to anchor off the coast of Panama to meet and transfer supplies and passengers. However, the plan for disembarkation is not yet finalized.
"While the onward plan for both ships is still being finalized, we continue to work with the Panamanian authorities on approval to transit the Panama Canal for sailing to Fort Lauderdale, Florida," the line said in the statement.
Holland America Line, along with major cruise lines worldwide, announced March 13 it would suspend cruise operations for at least 30 days and end its cruises in progress. But cruise ships that were at sea at the time were stuck on the water. They have been denied ports and scrambled to get passengers disembarked amid the coronavirus pandemic.
Thursday, an unspecified number of patients with "respiratory symptoms" on board the Zaandam were tested for COVID-19, two of which came back positive. Flu and respiratory symptoms and coronavirus symptoms are similar, so the cruise line told passengers to stay in their staterooms on Sunday.
Passengers will be separated based on their condition between the two ships.
"Today we announced a plan to transfer groups of healthy Zaandam guests to Rotterdam, with strict protocols for this process developed in conjunction with the U.S. Centers for Disease Control and Prevention (CDC)," Holland America's statement said. "Only those who have not been ill will be moved, and health screenings will be conducted before transferring."
A possible reason for dividing the passengers became clearer late Friday.
Holland America said the Zaandam arrived in Panamanian waters on Friday and has since been following the protocol of Panama's Ministry of Health, which states that if a vessel has individuals who have tested positive for COVID-19 on board, it cannot make any port operations or transit the Canal.
The healthy passengers transferred to the Rotterdam would likely be able to transit the Panama Canal and continue their journey back to the U.S.
Cruises viral outbreaks: Cruise lines had high rates of illness even before coronavirus
What's the protocol in a health emergency on a cruise ship?
According Cruise Lines International Association, member ships of the trade group meet health guidelines that include:
The ability to provide "reasonable" emergency care for passengers and crew members.
The ability to stabilize patients and begin "reasonable diagnostic and therapeutic intervention."
The ability to facilitate the evacuation of sick or injured passengers or crew members when "deemed necessary" by the ship's physician.
However, specific protocols vary by line, Bari Golin-Blaugrund, strategic communications director for CLIA, told USA TODAY Friday.
USA TODAY has reached out to Holland America Line about the cruise line's protocol for dealing with critical illness on board.
"As you can imagine ships don’t have a very sophisticated high level to deliver intensive care to more than a couple of people at a time," Jeffrey Ment, a travel industry lawyer, told USA TODAY Friday.
Liability, in this issue, is circumstantial, he said.
"You can have a bad outcome that’s not the doctor's fault," he explained. "Or you can have a bad outcome they're completely liable for."
All cruise ships are required to have a morgue on board – though they are generally very small, according to cruise publication Cruise Critic. Each can hold between three and six bodies, which can be kept in the ship's morgue for about one week.
The U.S. Centers for Disease Control and Prevention require that any ships that make port calls or have a home port in the United States report any death on board immediately.
Stress, uncertainty for passengers on board
Andrea Bergmann Anderson, 63, a passenger on the Zaandam from Maineville, Ohio, was waiting on Friday afternoon for a medical team to visit her cabin and give her a check up to see if she and her husband Rob, 70, would be among the healthy group able to transfer to the Rotterdam.
"I went to the medical center nine days ago because of the sinus infection and a cough," she said, adding she completed two rounds of antibiotics for the infection. Rob had also reported a cold to the medical center.She was feeling a bit nervous that she would not be allowed to transfer because of her visit to the center. "We filled out a medial form, and we were honest."
Then, just over an hour later, the news came: they did not pass the health screening.
Neither had a fever at the time of the screening and neither was asked to take a test for COVID-19.
"I am kind of depressed about this," she said. "I had hoped that we could go and that the ship would be clear to disembark. We could have lied, but that would not be right."
Holland America informed passengers of the deaths on board on Friday morning, Bergmann Anderson said.
Passengers over 70 will be transferred to the Rotterdam first, and quarantine will continue on board both ships until disembarkation. Anyone who has come in contact with an ill person will also remain on the Zaandam. All on board were provided with face masks when the ships met.
No one has been off the ship since March 14 when it was in Punta Arenas, Chile.
As for how the Holland America team has handled the possibility of COVID-19 spreading on board, Andrea said her assessment was they have gone "above and beyond" and taken every precaution.
"They really did everything possible," she said. "But if one asymptomatic passenger got on, there is not a lot that they can do."
And while she was upset that she and Rob were not allowed to transfer to the Rotterdam, she understood why and thought it was a fair decision. "They have be careful."
Now, uncertainty more than fear is causing her stress: Where and when will they get off the ship?
The questions don't stop with disembarkation. How she and Rob can get home remains up in the air, too, as does whether or not they'll need an additional quarantine period.
The Zaandam began its South American voyage from Buenos Aires, Argentina, on March 7 and was originally scheduled to end the sailing in San Antonio, Chile, March 21.
It stopped in Valparaiso, Chile, at the end of last week and has food and fuel for the remainder of the ship's intended journey to the U.S., the line said.
Holland America Line is offering complimentary counseling services over the phone through a crisis management service for passengers and crew members.
Contributing: Andrea Mandell
This article originally appeared on USA TODAY: Coronavirus: 4 dead, 138 sick on Holland America cruise in limbo