> The case remains under investigation, but it appears that someone became infected with the dengue virus, returned home and was bitten by a mosquito that passed it on to the local resident, according to Pasadena health officials.

https://abcnews.go.com/Health/wireStory/california-officials...

It seems part of the common pattern for outbreaks of dengue viral infections in other urban centres. However California lacks a non-human primate reservoir would probably limit the risk of it becoming endemic.