Helene Goldberg had been feeling unwell for days by the time she gratefully boarded an airplane in France bound for Atlanta on Friday, along with more than 300 other Americans and Canadians who had been stranded on a cruise ship in Europe carrying passengers with flu-like symptoms.

But because her temperature registered as normal when she landed, health officials from the Centers for Disease Control and Prevention allowed her to enter an Atlanta airport terminal and board a commercial airplane for Phoenix, carrying only instructions to quarantine herself for 14 days when she finally got home.

By the time she landed, her persistent cough had worsened, her fever had spiked and she was taken by ambulance to a hospital. Goldberg, 79, learned Monday that she had tested positive for the coronavirus, her son said in an interview.

Goldberg is one of a growing number of Costa Luminosa passengers who now have coronavirus or flu-like symptoms after flying back to the United States together on a chartered flight — a move that the travelers and their relatives say put others at risk. Many of the cruise ship travelers went on to board commercial flights in Atlanta.

Their experience is a sign that, even as many parts of the nation have entered near total shutdowns in an attempt to slow the outbreak, different standards about how to handle those at risk of being contagious may be allowing the virus to spread.

“The whole thing just doesn’t make any sense,” said Goldberg’s son, Matt, 46, who is now monitoring her health from his home in Louisville. He said that the cruise line and health officials should have done more to isolate returning passengers with symptoms. “They all knew. They had to have known.”

The handling of the Costa Luminosa passengers was dramatically different from the approach officials took toward the Grand Princess, a ship owned by Carnival Corp. In that case, passengers have been quarantined on military bases after 21 people aboard tested positive.

The Department of Health and Human Services said Monday that the first Costa Luminosa passengers who tested positive for covid-19, the disease caused by the coronavirus, showed no symptoms of illness when they boarded the charter flight back to the United States.

“For well travelers, it is part of CDC’s protocol to recommend that they continue expeditiously on flights home following disembarkation from cruise ships and chartered flights back to the U.S.,” the department said. “We gave passengers information at the airport about how to monitor their health, and advised them to immediately quarantine for 14 days after they arrive home.”

“Our guidelines have and will continue to change during each stage of a pandemic,” the department added.

At least four of the American passengers on the Costa Luminosa have tested positive so far, including three whose results came back while the plane was midflight. During the roughly eight-hour-long flight, multiple passengers had coughs and high fevers — and some lost consciousness, according to a former medic who was on board.

In the days since they landed, a Facebook page for passengers and family members has featured messages from those who say that since traveling home, they have developed fevers and coughs, the symptoms associated with the virus.

“Seat 24A. Low fever 99.5°-100°, sore throat, dry cough,” read one posting.

“Today my fever 38c, sore throat and runny nose. Seat 26j,” read another.

On Friday, CDC spokeswoman Kristen Nordlund said the airplane had been diverted to a remote part of the Atlanta airport and the three passengers whose tests were positive were isolated from others. A fourth was sent to a hospital for evaluation. She said all passengers were screened before they were allowed to leave.

“Passengers with no symptoms upon arrival were given health information advising them to stay home for 14 days after returning from travel, monitor their health, and practice social distancing as they continued to their final destination,” she said.

Roger Frizzell, a spokesman for Carnival Corp., which owns Costa Cruises, said guests had their temperatures taken and were released by French health authorities to disembark before boarding the plane; he said they were each provided masks as a precaution as well. In Atlanta, he said the CDC and Georgia health officials made decisions about how passengers were processed.

Health experts have said the cruise industry’s initial resistance to take drastic action as the virus spread — coupled with a deference from government officials, who let the companies come up with their own action plan — put passengers at risk.

A study published Monday by the CDC found that as of March 17, covid-19 cases had been linked to more than 25 different cruise voyages. The study showed that cruise ship-linked cases had been detected in 15 states and accounted for 17 percent of all known cases in the United States between the key early weeks of the spread from Feb. 3 to March 13.

On March 13, major cruise lines temporarily halted all new voyages, leaving dozens of ships out at sea, many of which are still seeking ports that will allow passengers to disembark.

On the Zaandam, a Holland America Line cruise ship, 42 people have reported to the ship’s medical center with flu-like symptoms. The ship, carrying more than 1,800 people, is not scheduled to reach land until it docks in Fort Lauderdale on March 30, but cruise line officials said they were exploring other options.

The first signs of problems on the Costa Luminosa began March 8, when a woman had disembarked in Puerto Rico complaining of trouble breathing and had been hospitalized. On March 14, the cruise line learned that the woman and her husband, who had been traveling with her, had tested positive for the virus. The next day, the ship quarantined passengers to their cabins and tried to dock in the Canary Islands.

But the Spanish government allowed only three passengers complaining of flu-like symptoms to get off and barred others from leaving the ship, forcing it back to sea in search of a nation willing to accept passengers.

On Thursday, the French government allowed the ship to dock in Marseille. By then, five passengers and two crew members had flu-like symptoms, Costa Cruises said last week.

The cruise line informed the 316 American and Canadians aboard that a charter airplane had been arranged to take them to Atlanta. As they disembarked, the passengers were screened by French health officials, who took their temperatures before they got on a bus to an airport.

The passengers desperately wanted to get home, several said in interviews.

Jenny Catron, a passenger and former medic who lives in Fredericksburg, Va., said she had noticed early on that many appeared to have a persistent cough.

“It was an act of mercy to try to get everybody home,” she said. “But anybody who has dealt with infectious disease would tell you it would not be advised to do what they did.”

Catron said the flight from Marseille to Atlanta was a horror. Passengers were not fed for hours before boarding and then provided only snacks on the long flight. After she realized some passengers were quietly losing consciousness at their seats, she said she began to perform health checks.

Catron and members of the flight crew isolated two men with high fevers away from other passengers in the first-class cabin, but she said there were shaky and ill people throughout the airplane and no medical personnel assigned to assist them.

She said that as far she knew, the three people awaiting test results were not kept separated from the rest of the passengers.

She said she tallied nine serious medical emergencies on board. An additional 20 to 30 passengers appeared to be showing coronavirus symptoms, Catron said.

At various times, she discussed with the airplane’s captain whether he should attempt to land early, but they agreed that there was little chance a foreign airport would agree to take symptomatic passengers.

In Atlanta, she said the plane was greeted by CDC workers wearing full protective gear. Many in the group assumed they would be medically evaluated and then escorted to military bases to be quarantined in isolation from the public, much as had occurred with passengers on the Grand Princess cruise ship, which docked on March 9 in Oakland after 19 crew members and two passengers had tested positive for the coronavirus.

But Catron said that after passengers had their temperatures taken and answered questions about possible symptoms, those deemed healthy were allowed to enter the airport, where they found tickets waiting for them to take them to other U.S. cities.

She said she refused. After being hospitalized in Atlanta and diagnosed with severe exhaustion, she said she is now self-quarantining at a hotel before returning home to Fredericksburg. But she fears her fellow passengers have now brought the coronavirus home to communities around the country.

“Every single person on that plane was covered head to toe in the virus,” she said. “They had been coughed on, sneezed on. They were covered in it.”

Hannah Sampson contributed to this report.