Northern California parents knowingly sent their COVID-19 positive child and a sibling to school last month in violation of isolation and quarantine rules, causing a coronavirus outbreak in an elementary school, officials said Saturday.

The child tested positive for the virus during the week of Nov. 8, according to Brett Geithman, superintendent of the Larkspur-Corte Madera School District. Both children continued to attend school the rest of that week and into the following week.

The child and their sibling, who later tested positive as well, are students in the district’s Neil Cummins Elementary School in Corte Madera, a town in Marin County that’s 15 miles (24.14 kilometers) north of San Francisco.

The parents did not notify the school of the positive test or return multiple calls from public health contract tracers, Geithman said.

The parents could face a misdemeanor charge for violating Marin County’s health order, under which people who test positive for the virus must isolate themselves for at least 10 days.

“Our enforcement team is evaluating the circumstances and will respond accordingly,” Marin County Public Health said in a statement. “Thankfully, this is the only known occurrence of a household knowingly sending a COVID-19 positive student to school.”

On Nov. 18, public health officials contacted the school district after they noticed a discrepancy in records, according to Geithman.

“We noticed you didn’t enter student X into the database” of students with COVID-19, Geithman said district officials were told.

The district immediately contacted the families of students who were exposed and told them to report to the school for rapid testing the next morning.

A total of eight students tested positive: The original student, their sibling, three classmates of theirs who are suspected school-based transmissions and three students who are suspected household transmissions. None of the students experienced serious illness or had to be hospitalized.

About 75 students were exposed to the virus from the eight cases, the superintendent said. No staff members tested positive.

Geithman said he did not know whether the original student and their sibling had received any doses of the vaccine.

The district issued a “corrective action” to the family but Geithman said he could not discuss what that was. The superintendent said the family caused a “safety risk” to students, staff and the school community that easily could have spread further over the Thanksgiving break if the exposed families had not been informed.

“This highlights that we are all in this together,” he said. “This is something where, to get through COVID-19, we all have to do our part. Our actions impact the health and safety and wellbeing of others.”

The district reopened for in-person instruction in October 2020 and this is its first case of classroom-based transmission, Geithman

“This one family, as troubling as it’s been, this is not the norm,” he said.

In May there was an outbreak at Our Lady of Loretto School, a private parochial elementary school also in Marin County, linked to an unvaccinated teacher. The teacher would unmask while reading aloud to students — despite an indoor mask mandate — and worked at the school despite a cough, fever and headache until testing positive later.

Altogether 26 other people — including students and their parents — were infected. A report by the Centers for Disease Control and Prevention, released in August, identified the virus in that outbreak as the delta variant.