The staff member was asymptomatic and the move was "out of an abundance of caution," the school said in a statement.
Students were dismissed early Wednesday for a deep cleaning of facilities, and school was closed until further notice, officials said.
The school plans on reopening March 16, however, that date could be further delayed in case of a mandatory, state-wide school closing imposed by New Jersey officials.
As of Thursday morning, there were 23 presumptive positive confirmed cases of COVID-19 in New Jersey, including one fatality. Ten of those cases were in Bergen County, others in Monmouth, Middlesex, Hudson and Burlington counties.
Several other schools had temporarily shut down for reasons similar to that of People's Prep.
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