LIVERMORE FALLS, Maine — Laboratory tests found that norovirus was the cause of about 25 children and staff at a summer camp becoming sick on July 10.

The state has cleared Camp Good News of Maine to reopen this weekend.

The camp was shut down on July 11 and about 100 campers and 80 staff members were sent home.

Dr. Sheila Pinette, director of the Maine Center for Disease Control and Prevention, said Wednesday that norovirus is highly contagious and fast-spreading.

“We do not know how norovirus came to the camp,” she said. That is still under investigation.

The virus causes the stomach or intestines or both to get inflamed and leads to stomach pain, nausea, diarrhea and vomiting, she said. It is sometimes referred to as the “ship” virus because it spreads so quickly.

Some campers and staff experienced nausea, vomiting and diarrhea two and a half hours after eating dinner at the camp on Schoolhouse Pond off Campground Road.

Health officials did not know whether the illness came from an infected person or from a contaminated food surface, food or sitting water, Pinette said. It also can be spread from hands not properly washed, she said.

Norovirus illness can be serious, especially for older adults and young children, according to the U.S. Centers for Disease Control and Prevention.

Norovirus is the most common cause of acute gastroenteritis in the United States. Each year, it causes about 21 million illnesses and contributes to about 70,000 hospitalizations and 800 deaths, according to CDC statistics. Norovirus is also the most common cause of food-borne-disease outbreaks in the United States.

People become dehydrated with the virus. It is important to drink plenty of liquids to replace fluids that are lost from vomiting and diarrhea, Pinette said.

“We commend the camp’s response,” she said.

Administrators and staff worked diligently to correct violations found after state licensing officials and epidemiologists went to the site to inspect it. Among the violations were equipment and food-contact surfaces and utensils not being clean, according to a state Department of Health and Human Services spokesman.

“They were very cooperative,” Pinette said. “I have to commend them for acting so quickly to close the camp.”

The camp will reopen to staff on Saturday and to campers on Sunday, she said.

The camp offers a range of activities, including canoeing, archery, swimming, fishing and riflery and is part of the Child Evangelism Fellowship of Maine.