NEW YORK (CBSNewYork) — Department of Health inspectors are checking out the cafeteria of a Queens elementary school after a number of children contracted a stomach bug.

About 28 students at PS 12 in Woodside reported feeling sick Thursday morning and were sent home. Their symptoms included nausea, vomiting and stomach pains.

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On Wednesday, some 60 students were sent home after complaining of the same symptoms.

“We think it’s the norovirus, which is fairly typical in winter, but obviously has had a very bad effect on that school community and on the kids there,” Mayor Bill de Blasio said.

Investigators testing surfaces in the school, however, have not yet found norovirus, CBS2’s Tony Aiello reported.

Nearly 20 percent of students — 200 kids — stayed home or left early.  The city believes some of those who stayed home were not sick, but were trying to avoid contracting the virus at school.

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People who’ve been inside the school say there are dispensers of hand sanitizer throughout the school and doors have been propped open to keep people from touching door handles, which could spread the virus.

“The teachers assured us they had sanitized everything, and we believed them,” said Joe Cross, a Native American storyteller who was giving a presentation at the school.

The school is located at 42nd Avenue near 72nd Street.

Though school remained open, de Blasio expressed concerns over other illnesses, WCBS 880’s Peter Haskell reported.

“Our message to any students and staff who are not feeling well: They should stay home,” the mayor said. “We want to help them get better, and we want to get a handle on this.”

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The school will be disinfected Thursday and again over the weekend, de Blasio said. Students went home with a norovirus fact sheet from the Department of Health.