According to the county's Health and Human Resources Agency, Pat & Oscar's in Encinitas and Mira Mesa have been identified after a review of probable poisoning cases.
Restaurants in Mission Valley, Carlsbad and El Cajon previously were identified as locations where the bacteria has caused infections.
Another case of E. coli has been reported since yesterday afternoon, bringing the total number of cases as of Friday afternoon to 34.
The victims, ranging from 17 months to 84 years old, are believed to have eaten tainted lettuce, either at the restaurants or when it was served to children at the San Marcos Unified and Alpine Union school districts.
The lettuce has been traced to an Orange County distributor called Family Tree, according to Health and Human Services.
The E. coli bacteria can cause severe abdominal cramping, bloody diarrhea, vomiting and nausea. If untreated, it can be fatal.
Last week Pat & Oscar's announced it would pay the medical bills of any customer who fell ill as a result of eating infected food at its restaurants.