It’s also because the strain of salmonella, Salmonella typhimurium, is common, so baseline cases of the disease were being reported before and throughout this investigation. The molecular subtyping pattern is also very common.
“So we don’t have a fabulous marker to tell if a person is clearly part of this outbreak,” Keene said. “That has slowed and hindered this investigation.”
Cases were reported across the U.S. and in Canada, although most were in the Western part of the country. Keene could not confirm whether any one state or any one shipper is suspected, but he did say at least one obvious lettuce growing state is involved.
“California is certainly a state where a lot of lettuce is growing, so it’s very interested. It’s one of the states involved,” Keene said Sept. 15. “At this point, nobody knows how the original contamination occurred. Even if it was shredded lettuce, there’s not a candidate field as of today.”
Keene said because the lettuce was shredded, there are also possibilities in the processing steps of the supply chain.
One thing that’s clear, Keene said, is that the outbreak is over. However, the CDC still classifies the outbreak as ongoing because of the baseline cases of this type of salmonella that will carry over. That makes it difficult to see a clear end in cases.
“So there’s no urgency now to do anything to protect consumers, but we’re still interested in finding out what caused this, whether it’s a deficient practice or just one more lettuce outbreak…” Keene said.
The Centers for Disease Control and Prevention and the Food and Drug Administration continue to investigate the cause of the outbreak, along with state departments of agriculture and public health.
The disease did not cause any fatalities, although two people were hospitalized, according to media reports.