The find brings the total number of infected batches discovered this year to six, and the amount of dead birds testing positive for the disease has also been increasing, according to the DEH.
"Mosquitoes are the main way people get exposed to West Nile virus," said DEH Director Elizabeth Pozzebon. "So remember to get rid of standing water around your homes so mosquitoes can't breed, wear insect repellent and report dead birds."
The three batches found in Jamacha, along the city limits with Lemon Grove, bring the mid-year total to a figure that equals that of all last year. The 2014 tally of 33 dead birds with WNV wasn't reached until November last year.
San Diego County residents were generally unaffected by West Nile virus until 2014, when 11 people were diagnosed with the disease and two died. More than 800 fell ill with WNV throughout the state last year, and 31 died.
West Nile virus is spread to birds and humans by mosquitoes, and the county has an eradication program in place. Residents are also encouraged to help out by dumping water out of outdoor pots and saucers, wheelbarrows, old tires and rain gutters.
Four out of five people bitten by a mosquito carrying WNV won't have symptoms. Of those who do get sick, most will have a mild headache, fever, nausea, skin rash or swollen glands.
The symptoms turn life-threatening in one out of 150 cases, mainly for people over 50 years old or those with weakened immune systems.