The fogging comes after 10 dead birds and six groups of mosquitoes that were collected from the eastern part of the county in the past week tested positive for West Nile virus.
Three of the dead birds were found in Antioch, three in Brentwood, two in Pittsburg and one in Oakley. Of the 46 dead birds to test positive in the county so far this year, more than half have come from Antioch.
The most recent positive mosquito samples were collected in Antioch, Brentwood and Oakley, areas that have continued to have higher numbers of West Nile positive birds and mosquito samples.
No human cases of the mosquito-borne illness have been diagnosed in the county so far this year, according to the district, but health officials are urging people to properly maintain their swimming pools and to drain backyard sources of standing water where mosquitoes can breed.
Truck-mounted fogging will be conducted tonight in two areas in Antioch and one in Brentwood.