Lettuce was the likely cause of an E. coli outbreak that sickened 94 people eating at a southwest Valley Federico’s Mexican Food restaurant, according to a report released by the Maricopa County Department of Public Health.

The outbreak occurred between July18 and 31 at the Federico’s, 13132 W. Camelback Road near Litchfield Park.

According to the report, the specific source of the bacterial exposure is uncertain, but lettuce is the most likely culprit.

“The lettuce could have been contaminated in the field from manure, or (from) contaminated irrigation water, during processing, transport, handling, or through improper storage,” the report states. “Improper lettuce washing and preparation at the restaurant may have contributed to the spread of disease. The restaurant corrected these processes and complied with all other recommendations and no new cases were identified, effectively ending the outbreak.”

In California, the investigation into the cluster of E. coli cases that sickened five Humboldt County residents — including county Supervisor Estelle Fennell — has been suspended, said public health director Susan Buckley of the county Department of Health and Human Services.

”We don’t have enough cases to identify a source,” Buckley said. “They occurred over a three-month period, and showed up sporadically since August.”

What made this cluster of cases unusual was that this particular strain of E. coli — known as O157:H7 — has not been reported anywhere else in California.

After interviewing the infected Humboldt residents, Buckley said that each individual ate leafy green lettuce before feeling symptoms.