When a local man arrived in a Boston emergency department on May 12 with an unusual mix of symptoms, doctors were scratching their heads for days.
It looked like monkeypox, a virus that causes symptoms including fevers, muscle aches, and a rash that turns into red bumpy pustules filled with yellowish fluid.
But the man had not travelled anywhere in the world where monkeypox was endemic.
“The patient … did not have any history of travelling to areas of Africa where monkeypox has been, or been in contact with animals,” Paul Biddinger, director of the Centre for Disaster Medicine at Massachusetts General Hospital, told the ABC News Daily podcast.
"And at that point there was not any history of people being diagnosed with monkeypox who didn't have that contact."
Four days later, reports emerged of patients with monkeypox in England who also had not travelled to areas of Africa where the disease was endemic.
"We said, 'Gosh, it's never happened in the United States before,'" Dr Biddinger said.
"It's almost never happened in the world before, outside of the recent reports in England, but we should really pursue it."
The clinical team in Boston moved the patient into a special part of the hospital that was created after the 2014 Ebola outbreak to care for patients with emerging infectious diseases.
Within days, the Centers for Disease Control and Prevention (CDC) confirmed it was the first case of monkeypox in the United States.
How did the virus spread?
Monkeypox is making headlines because it is spreading in an unusual manner.
According to Amesh Adalja, a senior scholar at the Johns Hopkins Centre for Health Security in Pittsburgh, it is most likely that visitors to Africa have travelled back to places like the US and UK, where they have spread the virus.
"There were two raves that occurred in Belgium — and people from all over the world may have attended that —and that seeded the virus into many different countries," Dr Adalja told ABC News Daily.
He said the outbreak was also unusual because it had predominantly impacted a single community group: "men who have sex with other men".
"So it's likely this origin is from a traveller who then has somehow passed it to someone who has gotten it into a social network, … [where it has then been ] magnified by certain events where people have multiple sexual contacts," he said.
"It's been able to exploit the close contact that occurs in those social clusters at raves, in saunas, other places like that, to be able to spread from person to person in a way that it hasn't had the opportunity to do so before."
He said while monkeypox was not classified as a sexually transmitted disease, it did require close and prolonged body contact with an infectious person to spread.
Doctors never suspected monkeypox
Medical professionals around the globe faced the same challenges in diagnosing monkeypox as those in Boston, according to Dr Biddinger from Massachusetts General Hospital.
"Where [the patient] travelled [and] who they've been in contact with really drives our thinking of what is possible and not possible," Dr Biddinger said.
Because most of the patients had no obvious link to outbreaks in central- and west-African nations where the virus is endemic, no-one suspected they could have had monkeypox.
In fact, if not for the news of the outbreak in the UK, the US doctors might never have diagnosed monkeypox.
According to the World Health Organization (WHO), monkeypox has now infected more than 780 people across 27 of its member countries.
Disease not at pandemic levels
Australia has recorded its seventh case of monkeypox, most recently in two men who returned to Sydney after travelling together in Europe.
NSW Health is undertaking contact tracing but has not identified any high-risk contacts so far.
The WHO said the monkeypox outbreak outside Africa would not lead to a pandemic, but it was considering whether the outbreak should be assessed as a "potential public health emergency of international concern".
Such a declaration, as was done for COVID-19 and Ebola, would help accelerate research and funding to contain the disease.
Last week it hosted a global research consultation with more than 500 experts, who recommended studies into the virus be expedited to better understand the spread, clinical consequences, and efficacy of vaccines.
