Between Friday, August 23 and Monday, August 26, 2013, the San Francisco Department of Public Health Communicable Disease Control Unit (SFDPH CDCU) received eight reports of laboratory-confirmed Escherichia coli (E. coli) O157 infection in unrelated San Francisco residents. This number of reports represented a marked increase over the background incidence of E. coli O157 in San Francisco of less than 1 case per month. The eight reports were received from three clinical laboratories. Case-patient residences were geographically dispersed throughout San Francisco but suggested moderate to high socioeconomic status. CDCU initiated standard follow-up interviews with all case-patients. While no common exposures or demographic characteristics were immediately apparent, cases tended to be younger, salad-eating, local-market shoppers.
On August 26, SFDPH requested assistance from the California Emerging Infections Program (CEIP), and an investigation was initiated to ascertain the source of infections and prevent further illnesses. The California Department of Public Health Microbial Diseases Laboratory (MDL) was asked to prioritize Pulse-Field Gel Electrophoresis (PFGE) testing of E. coli isolates from San Francisco and the surrounding counties. On August 28, 2013, a Health Alert was sent to local clinicians notifying them of the observed increase in cases, recommending increased testing for symptomatic patients, reminding them of the reporting requirement, and requesting forwarding of E. coli O157 isolates to the SFDPH Public Health Laboratory.
Case-patients were re-interviewed with a detailed hypothesis-generating questionnaire. The hypothesis-generating questionnaire identified a common restaurant and dates of exposure: Burma Superstar restaurant on August 16 and 17. On August 30, a joint press release was issued by SFDPH and Burma Superstar in order to inform the public and assist in case finding. A total of 22 confirmed and probable case-patients were identified. Confirmed cases shared an indistinguishable PFGE pattern combination, EXHX01.0124/EXHA26.0332. A case-control study and a dining group level cohort study were initiated to identify suspect food items. A garlic noodle dish was strongly associated with illness, but the specific ingredient causing disease was not identified. An environmental investigation resulted in recommendations for the restaurant that included improved hand washing and food handling, as well as a requirement for Food Safety training. See Final Report, Attachment No. 1.