Federal officials have reported they closed an investigation into an outbreak of E. coli O157:H7 infections linked to packaged leafy greens.

The outbreak sickened 10 people with four of the patients having symptoms so severe that they were admitted to hospitals. The four-state outbreak was linked to Nature’s Basket Power Greens and Simple Truth Organic Power Greens, according to the Centers for Disease Control and Prevention.

As of March 2, the Food and Drug Administration closed its investigation into the outbreak. The CDC has not yet updated its outbreak coverage, with the most recent information from the agency having been reported on Jan. 6.

During its investigation of the outbreak the CDC found that at least nine out of the 10 outbreak patients had eaten Nature’s Basket Power Greens or Simple Truth Organic Power Greens, purchased at grocery stores, before becoming sick.

The FDA reported that a traceback investigation of the leafy greens in the packaged salads led to farms in the Yuma, AZ, and Salinas, CA, growing regions.

“. . . no single production code was identified by the traceback.During FDA’s investigation, environmental samples collected near farms identified in the traceback in the Yuma, AZ, and Salinas, CA, growing regions tested positive for Shiga-toxin producing E. coli (STEC), however all were different strains and did not match the strain identified in this outbreak,” according to the FDA’s March 2 update.

In its Jan. 6 update the FDA reported no recall was initiated because it was believed that none of the salad remained on sale and no single source had been identified. The implicated salads had best-by dates through Dec. 20, 2021. As of its Jan. 6 update the FDA was continuing to investigate the outbreak.

“Some challenges encountered in this traceback are those often seen in tracing back leafy greens. These include multiple consumer purchases of the same product on different days, lack of product lot codes tracked to retail stores from distribution centers, and the inability to directly link product lot codes to consumer purchase data,” the FDA reported.

“Additionally, the range of possible production dates falls into the harvest transition period from central and northern California to southern California and Arizona growing regions, and as this product has multiple components, some production days of the product include ingredients co-mingled from multiple growing regions.”

Along with the CDC, state and local public health officials investigated the outbreak, which involved patients in the states of Alaska, Ohio, Oregon and Washington. Patient interviews revealed that a total of nine people reported eating Organic Power Greens with eight having eaten packaged salad sold under the Simple Truth Organic brand and one having eaten the Nature’s Basket brand. Both brands of Organic Power Greens have the same mix of leafy greens: organic spinach, mizuna, kale, and chard.

The implicated salads had best-by dates through Dec. 20, 2021.

As of its Jan 6 update, the CDC had found that patients’ symptoms began on dates ranging from Nov. 27, 2021, through Dec. 9, 2021. Sick people ranged in age from 26 to 79 years, with a median age of 59. All of the patients were female. One person developed a type of kidney failure called hemolytic uremic syndrome (HUS). The CDC has not reported whether a kidney transplant was performed.

“The true number of sick people in an outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because many people recover without medical care and are not tested for E. coli. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak,” according to the CDC.