Multiple California farms may have supplied the romaine lettuce contaminated with E. coli that caused an outbreak in late 2018, according to a report released this week.
The outbreak caused 62 reported illnesses, resulting in 25 hospitalizations. The Centers for Disease Control said the outbreak was over Jan. 9.
In November, health officials recommended lettuce growers withdraw all romaine from the market until the outbreak ended. By mid-December, officials had narrowed the source of the outbreak to three counties in central and northern California.
The particular strain of E. coli, O157:H7, was found in sediment from a water reservoir on a farm in Santa Maria, California, said the report, which was released Wednesday.
This single farm doesn't explain the entire outbreak, said Food and Drug Administration spokesman Peter Cassell. The reservoir was only used by one farm, but romaine from farms in all three counties tested positive for the E. coli strain.
The use of agricultural water from a reservoir has higher food safety risk than groundwater because pathogens are more likely to contaminate the surface, according to the report. The E. coli strain could have been present in the reservoir for months or years because the bacteria can survive longer in sediment than in overlying water, the report said.
The report said exactly how the lettuce came into contact with the contaminated water is uncertain, but it could have been through direct application to the crop or contact with the harvest equipment.
The investigation was conducted by the FDA, CDC, state authorities and Canadian officials.