The city closed two South Bronx schools Thursday morning after a student reported testing positive for the coronavirus. By Thursday evening, the city reported that the student had later tested negative, but the closures offered a first look at what actions city officials might take as students or school staffers report cases of the coronavirus.

The Laboratory School of Finance and Technology and South Bronx Preparatory: A College Board School, whose nearly 1,400 students share a building on East 145th Street, would remain closed for at least 24 hours, as required by the state.

Education department workers will “completely disinfect the building,” the mayor said. The city’s health department plan to locate the student’s close contacts and decide whether anyone else should be quarantined or tested. 

The mayor did not reveal the student’s age or condition. That student’s parent reported the positive test to the school on Thursday morning, de Blasio said, and the school was closed out of caution. The city later investigated and found the student had not actually tested positive for the coronavirus.

We don’t make this decision lightly, and we know the disruption and anxiety this means for students, faculty and parents,” de Blasio said in a tweet. “We are taking every precaution to keep people safe, and we will keep everyone informed as we learn more through the day.”

As of Thursday afternoon, the city had not found students at the schools with pre-existing conditions, who can be more vulnerable to the illness.

City officials have been resistant to the idea of closing schools en masse, noting that low-income families rely on the buildings for meals and childcare, as well as other services. 

Nearly 95% of students at both the Laboratory School and South Bronx Prep were from low-income families, according to data for the 2018-19 school year. They both serve higher shares of students with disabilities than the city average.

Students could pick up grab-and-go lunches at the school building’s main entrance, the education department said. 

Earlier this week, the state mandated closures for at least 24 hours at any school where a student or a staffer tested positive for the coronavirus — a move de Blasio said he agreed with. 

During that closure, city officials would be required to clean the school. Health department workers known as disease detectives would then be required to assess whether a longer closure is needed after figuring out who has had close contact with an infected person.

This story was updated to reflect the student later tested negative for the new coronavirus.