On May 22 the California Department of Public Health identified a cluster of Salmonella Thompson cases by PFGE. In the past, the PFGE pattern associated with this outbreak was only seen 5 times between 2012 and 2017 in the area. The PFGE pattern was most commonly associated with chicken in the past. Since the first case was identified in February 2018, approximately two cases with matching PFGE patterns were reported per week. Between April 6 and May 4, approximately 6.5 cases with matching PFGE’s were being reported per week.

In total, the outbreak included 39 confirmed cases. Cases ranged from 2-79 years old, and only 2 cases were under 5 years of age. 28 of the 38 cases (74%) were female. Most cases were residents of Modesto, California. 35 cases were symptomatic, and 6 cases were hospitalized for this infection. One case died due to causes other the Salmonella infection itself. 25 interviews were completed. Of the cases who could be interviewed, it was discovered that approximately 60 percent had eaten at El Pollo Loco in Modesto, California within 72 hours prior to onset of illness. All who reported eating at El Pollo Loco also reported eating a chicken dish there. 11 cases in total were found to be positive through urine culture, as opposed to stool culture.

On Friday, May 25 El Pollo Loco in Modesto, California was investigated. No obvious issues were detected from this inspection. On Thursday, May 31 environmental testing was conducted on 75 places in the restaurant and all staff were tested for Salmonella. The restaurant voluntarily closed on June 1, 2018 for cleaning, minor repairs, and staff clearance. One employee was found to have a similar Salmonella serogroup. A few environmental samples were positive for Salmonella, as well. The CDC assigned this outbreak the code 1806CAJP6-1.