The Connecticut Department of Public Health said Wednesday that it was norovirus that sickened customers at an Ellington doughnut shop earlier this month.
DPH lab tests confirmed the norovirus, according to the agency.
DPH said norovirus is a highly contagious virus that causes vomiting and diarrhea. The virus can be spread from person to person.
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Gerry's Donuts temporarily closed after getting reports of customers becoming ill.
An employee of the shop who spoke with NBC Connecticut earlier this week apologized for the outbreak.
Gerry's Donuts released a statement Wednesday that reads in part:
"The health department has informed us that we can reopen once we determine how the virus came about. We will follow their advice on any sanitizing procedures we’ll need to follow.
"The health and safety of our customers is and always will be number one with us. We want to reassure all of our loyal customers that we will do whatever it takes to get us all back together again safely and happily.
"We want to take a moment to express our deep gratitude for the dozens of customers who have reached out to us to offer their love and support. We now know how important we are to you. We have always known how important you are to us.
"Stayed tuned for the latest on our Facebook page. We’ll share what we know when we know it and let you know when we’ll be back.
"We can’t wait to open our doors and our hearts to all of you again."
It is not clear when Gerry's Donuts planned to reopen.