In December 2012 Minnesota Department of Health (MDH) and Anoka County Community Health and Environmental Services (ACCHE) investigated an outbreak of norovirus associated with romaine lettuce served at a restaurant in Blaine, Minnesota. The implicated meal date was December 11. Twenty-four restaurant patrons were interviewed. Four (17%) reported illness that met the case definition. No cases were hospitalized or sought medical attention. Three patron stool specimens tested positive for norovirus GI.

All four cases reported eating a salad made with either chopped romaine lettuce mixed with spring mix (n=2) or chopped romaine alone (n=2). In univariate analysis, consumption of romaine lettuce (4 cases versus 20 controls; odds ratio, undefined; p=0.01) was associated with illness.

ACCHE sanitarians interviewed 52 (65%) of 80 employees of the restaurant. Three reported recent gastrointestinal illness. No employees reported illness onset before the implicated meal date of December 11. No employee reported working while ill. No stool specimens were collected from employees for testing.

The restaurant had a routine inspection on December 6, 2012. At that time, both improper holding temperatures in the salad preparation refrigerator and a lack of supplies at several handwashing sinks were reported. During the evaluation conducted on December 17 as part of the outbreak investigation, all handwashing sink violations had been corrected and the salad preparation refrigerator had been serviced. Food workers preparing salads were observed wearing gloves and washing hands frequently. The spring mix served was pre-cut bagged product. Romaine lettuce was cut and prepared at the restaurant. daily.

The source of contamination of the lettuce was not identified. However, based on the presence of ill food workers after the implicated meal date, the plausible source of the contamination of the lettuce was an unidentified food worker.