Los Angeles county health officials have issued a warning to residents, telling them to be on the lookout for rabid bats.
The Department of Public Health said 21 rabid bats had been found in the county this year so far, twice the number typically found in the region.
Health director Jonathan Fielding said it was unclear why the number of rabid bats had increased.
Rabies is a viral disease that can cause death.
It was important for all residents to "understand the potential dangers posed to themselves and their pets, as most of these rabid bats have been found in and around homes", Mr Fielding said.
He urged residents to keep their children and pets away from bats and other wildlife.
One resident, who was attempting to nurse a bat back to health, was bitten and was treated for rabies, county officials said.