The second-largest foodborne outbreak of Shigella flexneri in more than 30 years struck guests at an Oregon wedding last August.

Shigella flexneri is a Gram-negative, enteric pathogen and together with three other Shigella species, Shigella dysenteriae, Shigella sonnei, and Shigella boydii is responsible for about half a million cases of shigellosis in the United States each year.

The source of the Shigellosi  contamination was not identified definitively for  the Aug. 11 wedding and reception in Oregon’s Yamhill County.

“Because humans are the natural reservoir for Shigella species, and there were no concurrent outbreaks to suggest upstream contamination, poor food-handler hygiene is the most likely cause,” says a recent Oregon Health Authority summary report.

Wedding and reception guest reports of gastrointestinal illnesses brought on an investigation by the Oregon Health Authority (OHA) and the Yamhill County Health and Human Services Department by Aug. 14.

Purpose of the investigation was to determine the cause of the foodborne outbreak and prevent additional cases. The Oregon Department of Agriculture, which regulates food -food service establishments joined the investigation.

A Health Alert Network notice was sent out on Aug. 15 after ten cases had been reports. It asked patients with gastrointestinal illnesses to submit stool samples and asked if they’d attend the Yamhill wedding and reception.

“Fecal samples from patients were cultured and isolates serotyped at the Oregon State Public Health Laboratory,” the summary report says.

On Aug.20, Shigella flexneri type 3a was first identified from a patient specimen. OHA consulted with subject matter experts at the Centers for Disease Control and Prevention (CDC) for information on this Shigella serotype,”

Yamhill County on Aug. 16 put up an online survey for guests attending the wedding and reception and contacted caterer for the event. The study collected data on foods consumed and the wedding and any illnesses that resulted.

A second online survey got underway on Aug. 20 after investigators learned there was a cocktail hour between the wedding and reception.

Out of 263 wedding and reception guests, 192 responded to the first survey and 128 to the second. Some people completed a survey for others, such as children.

The surveys were combined, showing 107 Shigellosis cases with 23 or 21 percent confirmed. The wedding and reception guests came from 12 states, with 82 or 77 percent being Oregon residents.

Persons attending the rehearsal dinner were no more likely to become ill than those who attended only the main event.

Reception service was buffet style. The epidemiologic investigation focused on food-exposures. “Five food items were each associated with a significantly increased risk of illness: asparagus, butter, bread, au gratin potatoes and the aioli that was served with the asparagus,” the report adds. “Asparagus was most strongly associated with illness: of those who ate asparagus, 64 percent became ill, compared to 12.3 percent of those who denied eating asparagus.”

Only bread remained significant when compared to asparagus.

No food-handling violations were discovered when Multnomah County inspectors visited the caterer. The caterer and its food handlers submitted stool samples, and all came back negative for Shigella.

The caterer’s records showed the same dishes were served at other events, but those did not result in illnesses. Asparagus was sourced locally. Water was tested for bacterial, and those tests were also negative.

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