In February and March 2017, an outbreak of norovirus occurred among residents and staff at a health system in Onamia, Minnesota. Illnesses were reported in all facilities, including the clinic, acute care, senior care, assisted living facility, and long-term care facility (LTCF). Several divisions within the Minnesota Department of Health were involved in the outbreak investigation.

Forty-three outbreak associated cases were identified among residents, including 20 in assisted living, 19 in LTCF, and 14 in senior care. Illness onsets dates ranged from February 16 to March 6. No one was hospitalized and no one died. Two stool samples tested positive for norovirus GI.4 Sydney.

A single vehicle of transmission was not identified. Multiple staff illnesses were reported prior to resident illness, and a peak in staff illnesses likely served as an amplifying event for transmission to residents. The pattern of illness onsets among residents and the illnesses among dietary staff indicate foodborne transmission likely played a role in the outbreak, in addition to person-to-person transmission.