Only one organism grew back. C. auris.

It was spreading, but word of it was not. The hospital, a specialty lung and heart center that draws wealthy patients from the Middle East and around Europe, alerted the British government and told infected patients, but made no public announcement.

“There was no need to put out a news release during the outbreak,” said Oliver Wilkinson, a spokesman for the hospital.

This hushed panic is playing out in hospitals around the world. Individual institutions and national, state and local governments have been reluctant to publicize outbreaks of resistant infections, arguing there is no point in scaring patients — or prospective ones.

Dr. Silke Schelenz, Royal Brompton’s infectious disease specialist, found the lack of urgency from the government and hospital in the early stages of the outbreak “very, very frustrating.”

“They obviously didn’t want to lose reputation,” Dr. Schelenz said. “It hadn’t impacted our surgical outcomes.”

By the end of June 2016, a scientific paper reported “an ongoing outbreak of 50 C. auris cases” at Royal Brompton, and the hospital took an extraordinary step: It shut down its I.C.U. for 11 days, moving intensive care patients to another floor, again with no announcement.

Days later the hospital finally acknowledged to a newspaper that it had a problem. A headline in The Daily Telegraph warned, “Intensive Care Unit Closed After Deadly New Superbug Emerges in the U.K.” (Later research said there were eventually 72 total cases, though some patients were only carriers and were not infected by the fungus.)

Yet the issue remained little known internationally, while an even bigger outbreak had begun in Valencia, Spain, at the 992-bed Hospital Universitari i Politècnic La Fe. There, unbeknown to the public or unaffected patients, 372 people were colonized — meaning they had the germ on their body but were not sick with it — and 85 developed bloodstream infections. A paper in the journal Mycoses reported that 41 percent of the infected patients died within 30 days.

A statement from the hospital said it was not necessarily C. auris that killed them. “It is very difficult to discern whether patients die from the pathogen or with it, since they are patients with many underlying diseases and in very serious general condition,” the statement said.

As with Royal Brompton, the hospital in Spain did not make any public announcement. It still has not.

One author of the article in Mycoses, a doctor at the hospital, said in an email that the hospital did not want him to speak to journalists because it “is concerned about the public image of the hospital.”

The secrecy infuriates patient advocates, who say people have a right to know if there is an outbreak so they can decide whether to go to a hospital, particularly when dealing with a nonurgent matter, like elective surgery.

“Why the heck are we reading about an outbreak almost a year and a half later — and not have it front-page news the day after it happens?” said Dr. Kevin Kavanagh, a physician in Kentucky and board chairman of Health Watch USA, a nonprofit patient advocacy group. “You wouldn’t tolerate this at a restaurant with a food poisoning outbreak.”

Health officials say that disclosing outbreaks frightens patients about a situation they can do nothing about, particularly when the risks are unclear.

“It’s hard enough with these organisms for health care providers to wrap their heads around it,” said Dr. Anna Yaffee, a former C.D.C. outbreak investigator who dealt with resistant infection outbreaks in Kentucky in which the hospitals were not publicly disclosed. “It’s really impossible to message to the public.”

Officials in London did alert the C.D.C. to the Royal Brompton outbreak while it was occurring. And the C.D.C. realized it needed to get the word to American hospitals. On June 24, 2016, the C.D.C. blasted a nationwide warning to hospitals and medical groups and set up an email address, candidaauris@cdc.gov, to field queries. Dr. Snigdha Vallabhaneni, a key member of the fungal team, expected to get a trickle — “maybe a message every month.”

Instead, within weeks, her inbox exploded.

COMING TO AMERICA

In the United States, 587 cases of people having contracted C. auris have been reported, concentrated with 309 in New York, 104 in New Jersey and 144 in Illinois, according to the C.D.C.

The symptoms — fever, aches and fatigue — are seemingly ordinary, but when a person gets infected, particularly someone already unhealthy, such commonplace symptoms can be fatal.

The earliest known case in the United States involved a woman who arrived at a New York hospital on May 6, 2013, seeking care for respiratory failure. She was 61 and from the United Arab Emirates, and she died a week later, after testing positive for the fungus. At the time, the hospital hadn’t thought much of it, but three years later, it sent the case to the C.D.C. after reading the agency’s June 2016 advisory.

This woman probably was not America’s first C. auris patient. She carried a strain different from the South Asian one most common here. It killed a 56-year-old American woman who had traveled to India in March 2017 for elective abdominal surgery, contracted C. auris and was airlifted back to a hospital in Connecticut that officials will not identify. She was later transferred to a Texas hospital, where she died.

The germ has spread into long-term care facilities. In Chicago, 50 percent of the residents at some nursing homes have tested positive for it, the C.D.C. has reported. The fungus can grow on intravenous lines and ventilators.

Workers who care for patients infected with C. auris worry for their own safety. Dr. Matthew McCarthy, who has treated several C. auris patients at Weill Cornell Medical Center in New York, described experiencing an unusual fear when treating a 30-year-old man.

“I found myself not wanting to touch the guy,” he said. “I didn’t want to take it from the guy and bring it to someone else.” He did his job and thoroughly examined the patient, but said, “There was an overwhelming feeling of being terrified of accidentally picking it up on a sock or tie or gown.”

THE ROLE OF PESTICIDES?

As the C.D.C. works to limit the spread of drug-resistant C. auris, its investigators have been trying to answer the vexing question: Where in the world did it come from?

The first time doctors encountered C. auris was in the ear of a woman in Japan in 2009 (auris is Latin for ear). It seemed innocuous at the time, a cousin of common, easily treated fungal infections.

Three years later, it appeared in an unusual test result in the lab of Dr. Jacques Meis, a microbiologist in Nijmegen, the Netherlands, who was analyzing a bloodstream infection in 18 patients from four hospitals in India. Soon, new clusters of C. auris seemed to emerge with each passing month in different parts of the world.

The C.D.C. investigators theorized that C. auris started in Asia and spread across the globe. But when the agency compared the entire genome of auris samples from India and Pakistan, Venezuela, South Africa and Japan, it found that its origin was not a single place, and there was not a single auris strain.

The genome sequencing showed that there were four distinctive versions of the fungus, with differences so profound that they suggested that these strains had diverged thousands of years ago and emerged as resistant pathogens from harmless environmental strains in four different places at the same time.

“Somehow, it made a jump almost seemingly simultaneously, and seemed to spread and it is drug resistant, which is really mind-boggling,” Dr. Vallabhaneni said.

There are different theories as to what happened with C. auris. Dr. Meis, the Dutch researcher, said he believed that drug-resistant fungi were developing thanks to heavy use of fungicides on crops.

Dr. Meis became intrigued by resistant fungi when he heard about the case of a 63-year-old patient in the Netherlands who died in 2005 from a fungus called Aspergillus. It proved resistant to a front-line antifungal treatment called itraconazole. That drug is a virtual copy of the azole pesticides that are used to dust crops the world over and account for more than one-third of all fungicide sales.

A 2013 paper in Plos Pathogens said that it appeared to be no coincidence that drug-resistant Aspergillus was showing up in the environment where the azole fungicides were used. The fungus appeared in 12 percent of Dutch soil samples, for example, but also in “flower beds, compost, leaves, plant seeds, soil samples of tea gardens, paddy fields, hospital surroundings, and aerial samples of hospitals.”

Dr. Meis visited the C.D.C. last summer to share research and theorize that the same thing is happening with C. auris, which is also found in the soil: Azoles have created an environment so hostile that the fungi are evolving, with resistant strains surviving.

This is similar to concerns that resistant bacteria are growing because of excessive use of antibiotics in livestock for health and growth promotion. As with antibiotics in farm animals, azoles are used widely on crops.

“On everything — potatoes, beans, wheat, anything you can think of, tomatoes, onions,” said Dr. Rhodes, the infectious disease specialist who worked on the London outbreak. “We are driving this with the use of antifungicides on crops.”