According to local media, 10 people went to the party in Santo Domingo, Valparaiso.
All 10 became infected with the virus - with the cat's owner believed to be patient zero - before they then passed it onto a further five others after the event.
While, thankfully, the cat never picked the virus up, it is understood that several of those infected became critically ill.
Francisco Alvarez, the Valparaiso Regional Secretary of the Ministry of Health (SEREMI), confirmed the outbreak during a public statement last week, telling local media that he hadn't believed the initial reports about to how the outbreak had started.
"When I heard it was a cat's birthday party I thought it was a joke," he said.
"That they were probably trying to hide something, but indeed it was.
"We have corroborated it with at least six of the 15 [infected] people who told us the same thing."
Alvarez added: "The cat never had the virus. It was the birthday organiser, the owner, she was patient zero."
The official said it was 'inconceivable' that an outbreak would occur in such a way, after authorities repeatedly told people to take the necessary precautions at gatherings with others - or, of course, to simply to stay home.
According to Meganoticias, Alvarez was at 'death's door' when he was previously infected with the virus.
It is not known whether or not authorities are still looking for potential cases through contract tracing.
While it's not clear when exactly the moggy celebrated its birthday (did it wait for the weekend, like some of us do to avoid being hungover at work?), officials have confirmed the cause of the spread.
While the cat didn't catch the virus from the event, other animals haven't been quite so lucky.
Since the outbreak of the pandemic, various animals have tested positive for the virus, including dogs, cats and even tigers.
Earlier this month, a group of gorillas in a zoo in the US were thought to be the first primates to have contracted Covid-19.
Staff at the San Diego Zoo Safari Park said that eight gorillas there had tested positive for the deadly disease, with a number of them having been seen to be coughing as a result.
According to park keepers, it's thought they caught the virus off a member of the park's wildlife care team, despite them following all 'safety protocols from the Centers for Disease Control and Prevention (CDC) and San Diego County Public Health', as well as wearing PPE whenever near the animals.
Speaking about the news, the park's executive director, Lisa Peterson, said: "Aside from some congestion and coughing, the gorillas are doing well.
"The troop remains quarantined together and are eating and drinking. We are hopeful for a full recovery."
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