An emergency room in Oregon has been quarantined after five people started experiencing hallucinations that appear to have been spread via touch.
The unidentified condition was first reported at around 3am last Wednesday, when a 54-year-old caregiver in North Bend Oregon phoned police complaining about seven or eight people trying to "take the roof off her vehicle".
Police investigated her house and couldn't find any evidence of the crime, but when the caregiver called about the incident again a few hours later, two Sheriff's deputies escorted her to the nearby Bay Area hospital to be examined for symptoms of hallucinations.
The woman was declared healthy and sent home, but pretty soon, one of the deputies who'd helped out with the case started hallucinating himself.
And then the second deputy, a hospital worker, and the caregiver's 78-year-old patient also began hallucinating, and were admitted to hospital.
All four had been in physical contact with the caregiver.
A Haz Mat team was deployed to both the hospital and the caregiver's residence, while the emergency room was emptied and quarantined to check for the source of the unidentified illness. Experts have so far been unable to locate a common source of contamination.
Blood tests of the affected patients also haven't turned up anything unusual.
Initially, police though that the hallucinations could have been caused by narcotic fentanyl patches, which are prescribed for chronic pain, and were worn by the caregiver's 78-year-old patient.
But they've since ruled that explanation out.
"Investigation has found that all those patches and potential medications that may have caused the symptoms have been accounted for," Coos County Sheriff's Office spokesperson Patrick Downing told KVAL News.
"The vehicles, equipment, and uniforms have been checked with no contaminates identified or located on or about them."
All patients have now been treated, released home, and have reportedly recovered - although the hospital worker is displaying some flu-like symptoms. The quarantine has also been lifted from the hospital.
But the investigation into the source of the hallucinations is ongoing, with police saying that the only thing they suspect for sure is that the illness was spread by direct contact.
However, it's not yet been ruled out that this isn't a case of mass hysteria - where many people in contact with each other all start to think they're suffering from the same physical condition, symptoms, or threat. It's possible that all these people who came in contact with the caregiver became so anxious that they also started hallucinating.
This is not the first time a mysterious illness has swept through a group of people, either - last year, dozens of children started fainting during a Remembrance Day ceremony in the UK. In that case, the suspected cause appears to have been a simple been a case of heating and widespread panic about children becoming ill.
We'll be watching for updates on this latest case closely.