Merced and San Joaquin counties reported human cases of West Nile virus in the past few days.
Merced officials would say only that the patient is younger than 18; where he or she lives was not released.
In San Joaquin County, health officials confirmed that a 48-year-old Stockton man is the first human with the virus there this year. The man reported having no symptoms, but tested positive for the virus when donating blood. Although for reporting purposes this does not meet the definition for the California Department of Public Health to count it as a case, it indicates there is active transmission of West Nile virus to people in San Joaquin County.