By Jacqueline Howard, Norma Galeana, CNN

(CNN) — The US Centers for Disease Control and Prevention has declared that this summer’s outbreak of cyclosporiasis tied to iceberg lettuce has ended, as of Friday, marking a significant public health moment.

The federal update, released Friday morning, adds that while the outbreak is over, the US Food and Drug Administration will continue its investigation of cyclospora infections linked to iceberg lettuce sourced from central Mexico and recalled by Taylor Farms de Mexico.

“FDA remains confident that all recalled iceberg lettuce related to this specific Cyclospora outbreak is off the market,” the agency said in Friday’s update. “Although the outbreak is over, FDA’s outbreak investigation remains ongoing. FDA will continue to work with federal, state, and international partners to complete its investigation and will provide updates as they become available.”

The outbreak, spanning 21 states, has sickened at least 12,883 people, among whom 570 have been hospitalized and two died, according to the FDA and CDC, as of Friday.

The outbreak grew to be the largest on record in the US.The hardest-hit state was Michigan, where about 1 in every 1,000 people had cyclosporiasis.

Investigators said data pointed them toward shredded iceberg lettuce associated with illnesses in people who reported eating at some Taco Bell locations. The FDA traced the lettuce to the company Taylor Farms and growers based in Mexico. In mid-July, Taylor Farms de Mexico announced that it had removed all iceberg lettuce sourced from central Mexico from the US market, and Taylor Farms began a recall.

The FDA noted that most of the illnesses tied to this outbreak began before the Taylor Farms iceberg lettuce recall was announced July 17.

In Friday’s update, the FDA said that its “onsite inspections and sample collection at iceberg lettuce growers and the processing facility in Mexico, in coordination with Mexican officials, have ended. Samples from the onsite inspections are pending analysis.”

The Taylor Farms facility in Doctor Mora, Mexico, remains closed with no reopening date, a worker told CNN. “The only people at the plant are maintenance workers servicing equipment,” the person said.

The person also said field workers were told they may be able to return Monday but are still awaiting confirmation.

The Taylor Farms plant in Doctor Mora has not processed any food packaging since about July 10, when workers were called in to destroy bags of lettuce that had been returned after being shipped to the US.

When someone is infected with cyclospora, the microscopic parasite that causes cyclosporiasis, they can develop explosive diarrhea along with other intestinal symptoms – and it can take two days to two weeks for symptoms to appear. It can also take as long as six weeks for CDC and state health officials to determine whether an illness was connected to the outbreak, according to the FDA. As a result, there can be a lag in when a case gets reported after someone is exposed to the parasite.

“There is quite a delay between when the contamination occurred versus when people were actually consuming this and then them actually reporting sick,” Matthew Moore, an associate professor of food science at the University of Massachusetts Amherst, said last month.

“It sounds like all the product that was implicated, at least as far as we know, has been recalled,” he said. “Unlike some other pathogens like salmonella – that potentially could be person-to-person, where you have an initial spike that’s getting people sick, and then they’re getting other people sick, where you could potentially continue the outbreak – with cyclospora, because it’s not transmitted person-to-person, it’ll just kind of die off.”

Federal health officials were expected to declare the outbreak over once they’re confident that new illnesses are no longer emerging, Dr. Colleen Kraft, a professor of infectious diseases at Emory University School of Medicine, said in an email last month.

“They also need time for recently diagnosed cases to work their way through laboratory testing, patient interviews and epidemiologic linkage,” Kraft said. “Essentially the immediate consumer risk from the recalled product appears to have passed.”

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