Outbreak of Norovirus Gastroenteritis Associated With Ice Cream Contaminated by Frozen Raspberries From China-Minnesota, United States, 2016.

BACKGROUND

Norovirus is the etiology for about 60% of foodborne outbreaks identified in Minnesota. Contamination of food during preparation by food handlers is by far the most common cause of these outbreaks. Norovirus outbreaks due to commercially distributed foods are rarely reported in the United States, and only 2 have been previously identified in Minnesota, both due to oysters.

METHODS

In August 2016, we investigated an outbreak of norovirus gastroenteritis in Minnesota that was linked to consumption of commercially distributed ice cream at multiple venues. Sanitarians from local public health agencies visited the facilities involved for follow-up, and case-control studies were conducted. The outbreak was identified by linking multiple independent illness reports to a centralized foodborne illness complaint system and subsequently confirmed though genotyping of stool specimens.

RESULTS

A total of 15 cases from 4 venues were reported. Raspberry chocolate chip ice cream was statistically associated with illness in 2 analytic studies (6 of 7 cases vs 0 of 7 controls; odds ratio, undefined; P = .005). Norovirus GII.17[P17] (GII.17 Kawasaki) strains from case stool specimens matched norovirus found in frozen raspberries imported from China that were used to make the implicated ice cream.

CONCLUSIONS

To our knowledge, this is the first norovirus outbreak due to commercially distributed frozen berries identified in the United States. To detect norovirus outbreaks associated with commercially distributed food vehicles, investigators should thoroughly investigate all norovirus outbreaks (including stool testing and genotyping), coordinate complaint and response activities across agencies and jurisdictions, and consider testing food for norovirus when appropriate.