Student and school employee in Barnstable also being tested.

Cape officials on Tuesday announced a third case of COVID-19 in Sandwich as well as the testing of a student and school staff member in Barnstable who have symptoms of the new coronavirus.

The latest person to be diagnosed in Sandwich is a person in their 80s who had contact with a married couple from the town whose diagnoses were confirmed during the weekend, Sandwich Health Agent David Mason said.

“The cases are all contacts,” Mason said.

Town officials went through the process of contact tracing for each of the ill individuals. “All direct contacts for each case in the town of Sandwich have been notified,” Assistant Town Manager Heather B. Harper said in a statement Tuesday afternoon announcing the third case.

“We expect the virus will continue to appear throughout the region and in our community,” Harper said while appealing to people to practice social distancing and routine handwashing.

“Only go out when you need to,” she said.

Read more coronavirus news on Cape Cod

Also Tuesday, Barnstable schools Superintendent Meg Mayo-Brown announced that a student at West Villages Elementary School in Marstons Mills and a staff member at Barnstable High School in Hyannis were being tested for COVID-19 after developing symptoms.

Both individuals are in self-quarantine, Mayo-Brown said in the notice to the school community posted on the district's website.

Barnstable public schools, which are closed until at least April 7 as part of a statewide order by Gov. Charlie Baker, will be deep-cleaned starting next week, Mayo-Brown said.

Cancellations related to COVID-19 on Cape Cod and the Islands

She asked that anyone who has a child in the school district who undergoes testing reach out confidentially to nursing and wellness coordinator Pam Ciborowski. She also again asked all parents and students to practice social distancing.

“We know that it is difficult for children to be away from their friends and extended family, but it is the only reliable way to slow the spread and protect all our vulnerable community members,” Mayo-Brown said.

The news follows Mayo-Brown’s announcements this past weekend that a Barnstable Community Innovation School staff member and her husband, both residents of Sandwich, had tested positive for COVID-19, the disease caused by the new coronavirus.

The announcement about the husband, who is in his 60s, came Saturday, followed by the news Sunday that his wife also had contracted the disease. Mayo-Brown said the woman has been out of school since March 6 and asked all students and staff who may have been in contact with her to quarantine themselves until Friday.

Asked if coronavirus transmission had reached the point of community spread, Mason said, “It’s going in that direction.”

The Trump administration this week called on Americans to take 15 days to slow the spread of the virus by working from home, avoiding social gatherings of more than 10 people and postponing shopping trips and travel.

Public health officials seek to reduce and spread out the cases of the virus — called flattening the curve — so hospitals are not overwhelmed by a peak demand for beds and ventilators as occurred in countries such as Italy.

As of Tuesday afternoon, the state Department of Public Health reported 218 confirmed cases of COVID-19 in Massachusetts.

The numbers did not include the third case in Barnstable County. “Case counts are finalized and posted once per day, so the counts may lag by up to 24 hours,” department spokesman Omar Cabrera said.

The confirmed cases are likely the tip of the iceberg, said Dr. Donald Thea, director of the Center for Global Health and Development at the Boston University School of Public Health.

He estimated that the number of cases is 10 times what is currently being reported.

Mobile testing sites that have opened in West Barnstable and Nantucket this week already have tested dozens of patients for the virus.

By late Tuesday afternoon, nurses and technicians from Cape Cod Healthcare and Barnstable County had swabbed the nasal passages of about 30 patients who had pulled up to a mobile testing unit in a Cape Cod Community College parking lot, according to Cape Cod Healthcare spokesman Patrick Kane.

Four people were tested Monday as the mobile site was gearing up for its first full day of business Tuesday. Another 75 patients had appointments to be tested later Tuesday and into Wednesday, Kane said.

The new mobile site is open from 8 a.m. to 6 p.m. daily. Patients need a doctor’s order and an appointment to be tested.

Cape Cod Healthcare officials directed people experiencing serious symptoms who do not have a primary care physician to triage tents in front of Cape Cod and Falmouth hospitals.

The officials said “patients displaying symptoms of COVID-19 including fever, coughing or shortness of breath should contact their primary care provider to be screened for COVID-19.”

For information on the testing site, go online to capecodhealth.org/coronavirus.

Drive-thru testing sites also have been set up this week in Boston, Braintree and Peabody, and more sites are expected to open up.

Children and young adults are not at as high risk of getting severely ill from COVID-19 as older adults, but school transmission is a problem when youngsters come in contact with older adults in the community and people with medical conditions such as diabetes, Thea said.

“It’s very, very important to keep those populations segregated,” Thea said.

Follow Cynthia McCormick on Twitter: @Cmccormickcct.