Mosquito samples taken from Santa Ana, Costa Mesa and Dana Point have all tested positive for the virus.
These cities have been added to a growing list topped by La Habra, which has 15 recorded samples testing positive for the virus, Orange County Mosquito and Vector Control District officials said.
Two years ago, Santa Ana was "more or less the epicenter of West Nile virus activity," said Jared Dever with vector control. However, the city has not had any positive samples until two batches tested positive on Tuesday, he said.
Anaheim has recorded five positive samples of the virus, and the city of Orange has had three so far, Dever said.
Garden Grove, La Palma, Mission Viejo, Tustin, Stanton, Mission Beach, Yorba Linda, Seal Beach and Irvine are also showing signs of West Nile.
But so far, there have been no reports of the virus being transmitted to people.
Vector control officials recommend the following steps for protection:
- Dump or drain any standing water
- Repair window and door screens
- Apply repellent when outdoors
- Avoid spending time outdoors at dawn or dusk
City News Service contributed to this report.