A third person at the Mabel I. Wilson elementary school in Cumberland has tested positive for the coronavirus, the superintendent of schools announced in a letter to parents Monday.

The person as a staff member at the school, which is attended by 690 students in kindergarten through grade three, said Jeffrey Porter, superintendent of Maine School Administrative District 51, which serves Cumberland and North Yarmouth.

“I am writing to let you know of a third positive test result for the coronavirus within the school community, now a second staff member at Mabel I. Wilson School,” Porter wrote. “As with my last communication on Friday, there is not enough information available to rule in or out the possibility of transmission of the virus to others during the last week that school was in session.”

Porter noted that it has been 16 days since school ended March 13 and that public health officials say symptoms of the virus typically emerge within 14 days, with a recommended buffer of 48 hours beyond the 14-day period.

Due to privacy laws, Porter told the school community that he would be unable to identify the staffers who have tested positive. However, he said he will inform the school community of any additional positive test results are confirmed.

“Please know that my commitment to balancing these two considerations means I am unable to disclose information other than what is stated in this communication,” Porter said.

In a telephone interview Monday evening, Porter said he hasn’t been able to get in touch with the state to determine if there are more students or staffers from Mabel Wilson School who have tested positive for the virus. He found out Monday from the infected staffer.

Porter said he has been in touch with superintendents in Maine and said he is unaware of any other school district that has had three COVID-19 cases in one school.

“I am concerned, especially when you have three people in one building,” Porter said. Part of his concern is that he does not know when the three individuals contracted the virus.

“We don’t know because they don’t know,” said Porter.

On Friday, Porter announced that another staffer at the school on Tuttle Road had tested positive. School officials said they can’t rule out the possibility that the staff person transmitted the virus to other individuals during the last week school was in session.

Porter told the school community last Thursday that a student at Mabel I. Wilson tested positive, and offered some details based on an investigation by the Maine Center for Disease Control and Prevention. Porter said the CDC determined the student appears to have been exposed to the virus outside the school after it closed and had not been in contact with other students.

Porter said anyone else from the school district who tests positive for the virus should contact him immediately.

Most of Maine’s public schools will remain closed until at least April 27, with most districts using online learning programs to educate students.

As of noon Monday, the Maine CDC was reporting 275 confirmed cases of coronavirus in Maine, with three deaths and 49 people hospitalized. Cumberland County, with 154 cases of COVID-19, has the most confirmed cases of any in Maine.