Amid a deluge of fresh details about a possible “super-spreader” of the new, deadly coronavirus, public health experts questioned whether the same kind of ultra-contagious patient may be responsible for the largest outbreak outside China: a cruise ship off the coast of Japan.

The potential existence of coronavirus super-spreaders, unusual in any epidemic, also bolstered a lingering suspicion by some public health experts that people who have not yet experienced symptoms can spread the fatal disease.

The global death toll for the novel 2019 coronavirus surpassed 1,000 on Monday, with at least 42,500 confirmed cases. The vast majority of infections—and all but one death—have occurred in mainland China or Hong Kong, while the number of people infected in the United States reached 13 after a new case was confirmed in San Diego on Monday.

But international attention has recently homed in on the case of a 53-year-old British man deemed a “super-spreader,” or a person who transmits the virus more efficiently than average. In this case, the individual appears to have passed the disease to at least 11 people in three countries during a trip from Singapore to France to Switzerland to England.

“This British super-spreader had no symptoms during his period of transmission,” said Dr. Adrian Hyzler, the chief medical officer for Healix International, which provides medical information to organizations whose clients travel internationally. “He has really set in motion a web of infections.”

In disease outbreak analysis, officials measure the transmission of an infection by looking at the “reproduction number” or “R0.” Essentially, a R0 of 1 means the average person who gets a disease will transmit it to one other person; an R0 of 2 means the average person with the disease will transmit it to two other people. For the novel 2019 coronavirus, the World Health Organization has estimated an R0 between 1.4 to 2.5, while a group of Chinese doctors calculated it to be between 3.3 and 5.47 in the International Journal of Infectious Diseases last month.

“The aim through public health measures is to get the R0 less than 1, which means that we can contain the virus,” said Hyzler. A super-spreader is anyone who infects a higher number of people than the R0.

Irwin Redlener, director of the National Center for Disaster Preparedness at Columbia University and an expert on U.S. readiness for pandemics, told The Daily Beast that the possible existence of super-spreaders in the coronavirus epidemic is “very unusual.”

“It means someone is excreting the virus more much efficiently,” Redlener said. “When a person who is a super-spreader coughs, a lot more virus is excreted, and the spread is much more rabid just because more people get sick who come in contact with a super-spreader.”

So far, in the United States, even among those who have transmitted the virus person-to-person, only spouses have been confirmed to have the virus. But a super-spreader represents a whole other level of risk, experts said.

“In a non super-spreader, if we find that there’s 20 people that now need to be checked, with a super-spreader it might be multiples of that: 40 or 60 people,” Redlener told The Daily Beast on Tuesday. “We just don’t know how many super-spreaders there are out there, so it makes tracking incredibly difficult.”

Public health authorities do not know why some people are super-spreaders and others are not, despite the phenomenon recurring during various outbreaks over the years.

“They came to prominence during the SARS epidemic, but they have been around since the last century at least,” Hyzler said. “We can only speculate as to the effect of super-spreaders in [the coronavirus epicenter of] Hubei because you need a fully equipped epidemiological research team to put together all the pieces with time consuming detective work, and that is just not possible in China where they are trying to hold back a tsunami of sick people in an overwhelmed healthcare setting.”

Jeremy Brown, director of the Office of Emergency Care Research at the National Institutes of Health and the author of Influenza: The Hundred-Year Hunt to Cure the Deadliest Disease in History, said the “classic example” of a super-spreader can be found in the case of “Typhoid Mary,” the infamous woman who did not get ill herself but transmitted the bacteria that causes typhoid to others.

But Brown also used the case of “Typhoid Mary” to sound a note of caution in hyping the dangers posed by alleged coronavirus super-spreaders.

“By the time she died in 1938, she is thought to have infected at least 50 other people,” said Brown. “But she is well known precisely because her story was so unusual. It seems to me to be very premature to give this title to a person in connection to the coronavirus.”

But Hyzler argued the sheer number of cases on the quarantined, Yokohama, Japan-based Diamond Princess cruise—at least 135, 23 of them Americans—pointed to the possibility that a super-spreader brought the disease on board before disembarking in Hong Kong.

The passengers and crew members have been quarantined on the 3,700-person ship since Feb. 3, and Japanese officials have reportedly said they cannot test everyone on board. There are approximately 400 Americans on the ship, where passengers are confined essentially to their quarters, some of them claiming they don’t have windows.

“It seems certain that this was caused by a super-spreader who has caused absolute mayhem through no fault of his own,” said Hyzler, noting that even if the individual in question left the ship, other super-spreaders could still be on board. “It is very surprising that with the isolation conditions there are still so many cases—this is either due to a longer incubation period or another super-spreader.”

But if there are multiple super-spreaders on board the ship, we won’t know until research epidemiologists are able to investigate and create a detailed web of diagrams linking the cases, Hyzler said.

Redlener agreed that a super-spreader may well prove responsible for the situation on the Diamond Princess.

“That cruise ship is in some ways an example of the worst case scenario,” Redlener said. “If the index case is a super-spreader, we have a bigger problem than most of us thought we were going to have. If people were asymptomatic, they were likely hanging out together in common spaces and having no idea that one or more people on the ship were infected.”

“I would be concerned about every human being on the ship,” he added. “Every single person on that ship is in danger of becoming infected, and they all need to be tested. The key thing right now is to find the negatives—and get them off the ship—and then track and quarantine the positives.”

Though both Hyzler and Redlener said the situation on the cruise and elsewhere has raised concerns that the incubation period for the virus may be longer than what the CDC and WHO had described—between 2 and 14 days—the Diamond Princess was essentially adhering to the same quarantine protocol as the U.S. government.

In a statement this week, the cruise line said that it was following the guidance of the Japan Ministry of Health on medical care and disembarkation protocols. The quarantine was slated to end on Feb. 19, unless there were unforeseen developments, according to the statement.

The company did not answer questions from The Daily Beast about why passengers who have tested negative were still on board the ship, gaps in testing, or whether they have questioned the 14-day quarantine, deferring all questions about those issues to the Japanese government.

Japanese officials have said they tested approximately 439 people on board as of Monday but that the logistical challenges of testing all crew members and passengers were too difficult to overcome, especially considering that the government wants to keep some test kits in the event of an outbreak inside the country. Testing everyone on board might also delay the quarantine unduly, Japan’s health minister, Katsunobu Kato, said Monday.

Despite that reasoning, Redlener went so far as to call the cruise a “biologically toxic environment,” where anyone on board is in “significant danger” every day they remain on the vessel.