Two banquet servers at a Green Mill restaurant were the possible sources behind an April outbreak of Salmonella Braenderup infections. But, the Minnesota Department of Health (MDH) today reported other sources cannot be ruled out.

Seven laboratory-confirmed illnesses were associated with the outbreak among people who ate food from the Bloomington, MN, restaurant. Another seven people met the outbreak profile but were not lab confirmed.

Two clinical Salmonella Braenderup isolates were picked up on April 19 during routine testing. They had indistinquishable pulsed-field gel electrode (PFGE) patterns. It was the Minnesota PFGE pattern BR134.

The final report by MDH on the outbreak was released today. The Bloomington restaurant is one of 23 Green Mill locations.

Interviews with sick people pointed MDH and the Bloomington Environmental Health Division toward the Green Mill Restaurant and Bar.

Green Mill customers were reporting diarrhea and fevers lasting at least three days after dining at the Bloomington restaurant.

“Stool samples collected from consenting individuals were submitted to the MDH PHL (Public Health Laboratory) for bacterial and viral testing,” the report says. “PFGE and whole genome sequencing (WGS) was performed on isolates.”

The MDH collected online orders, information for catering groups, and receipts for April 5, 8, 9 and 10. To find additional cases and controls, MDH personnel called all the known patrons.

The health department required all Green Mill employees to submit two stool samples for Salmonella testing. Any employees reporting an illness on or after March 15 were excluded from foodservice work until they produced two consecutive stool samples with negative results.

Employees who tested positive for Salmonella by culture were excluded until two consecutive stool samples tested negative.

The state health department interviewed 89 Green Mill patrons and 18 attendees from a catered training event. Two partrons reported illnesses that did not meet the outbreak criteria. They were not subjected to further analysis.

The meal dates and the number of cases were: March 22 with one illness reported; April 5 with 3; April 8 with 4; April 9 with 3; and April 10 with 3. Four cases had two or three meal dates. Onset dates of illnesses ranged from March 29 to April 16.

Ages of the sick people ranged from 6 to 65 years, with the median being 39 years old.
Fifty-seven percent of the ill were male.

All seven lab-confirmed patients reported diarrhea and cramps, 71 percent experienced fever, and 14 percent or one case each reported vomiting and bloody stool.

No one died or required hospitalization, but four of the seven, or 57 percent, did visit a healthcare provider. The median incubation period for three cases with a single meal date was 115 hours.

Three of the laboratory-confirmed cases involved attendees of a training event on April 8, 9 and 10 that was catered by Green Mill.
The others either ate in the restaurant or picked up take-out orders.

Further analysis pointed to tomatoes and romaine lettuce as being associated with the outbreak. Health department officials interviewed all 53 restaurant employees.

The report says sanitarians identified a number of issues. These included how the sink was plumbed, empty tower dispensers on the cook line, employees touching pizza with bare hands, and the rinsing of a pizza cutter in the hand sink. Also, a pressure gauge was not working on the dishwashing machine.

Finally, MDH reports Green Mill received tomatoes and romaine lettuce deliveries on the morning of April 5.

The first Green Mill opened in St. Paul, and later became known for its deep dish Chicago-style pizza.