SEBEC – State health officials believe a “Norwalk-like” virus was what caused a large number of people to become ill last week after swimming in Sebec Lake at Peaks-Kenny State Park.

More than 40 people were sickened with diarrhea, vomiting and stomach cramps on Thursday and Friday, according to Geoff Beckett, chief of infectious diseases at the Maine Bureau of Health.

The illness appears to have been caused by a “Norwalk-like” virus, a family of viruses that is transmitted by water or food, according to Beckett. It’s basically a “self-limiting illness” that has a one- to two-day incubation period and the symptoms last 12 to 18 hours, he said.

A combination of factors appeared to have played a role in the outbreak, including the shallow, sheltered beach, the hot weather, the large number of people who flocked to the beach and a fecal accident that occurred at the park Wednesday, according to Beckett.

“The outbreak appears to be over,” Beckett reported Sunday.

Once the outbreak was known on Friday, park officials posted an advisory. When no new reports of the illness surfaced over the weekend, the park removed the advisory with approval from the Bureau of Health.

Beckett said his department uses a generic E. coli test to determine the presence of bacteria in the water and the E. coli is not the type that causes severe illness. However, he said, this outbreak sounded like it was virus-related, not bacteria-related.

Lifeguards at the park observed some fecal matter floating in the water Wednesday and reported it to park officials. That fecal material may have triggered the virus, according to Beckett.

Beckett said the lake water was suspect because it was the only common denominator among the people who became ill.

No one was hospitalized from the illness, he noted. The drinking water also was tested, and although a coliform colony was present, he doubted this caused the outbreak. The water will be rechecked, but Beckett noted that the well water had been of consistently good quality since it was installed. Had it been the well water, he said, other people would have become ill since Wednesday.

“The key is that this appears to have been an incident that occurred at a particular time and has since dissipated,” Beckett said. There is no reason to expect it will continue to cause problems, nor will it cause problems in other areas of the lake, he said.

Park Manager Bill Elliot said he was notified Friday that about 40 of the 100 or so youngsters and adults from the Bangor YWCA became ill with vomiting, stomach cramps and diarrhea. He said one of the adult callers told him that her physician said a “24-hour bug” had been making its rounds in Bangor and that could have caused the outbreak.

Learning of the outbreak, Elliot said he took samples of the lake water Friday and delivered them in person to the bureau’s laboratory in Augusta. Upon his return, he discovered that some children from East Corinth, who had been at the park Wednesday, also became sick.

Beckett’s department also received calls from eight to 10 other parties who were at the park on Wednesday and who became ill later with the same symptoms.

Elliot appeared to have doubts that the illness was caused by the lake water. He said his daughter and park lifeguards had been in the water last week and were not affected. In addition, several park visitors ignored the posted warning and were swimming after the incident, he said.