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WINSTON-SALEM, N.C. — A suspicious substance was delivered to a Winston-Salem school.

Officers were called to Calvary Day School on Country Club Road Thursday morning.

They say someone there opened a letter containing an unknown substance which caused a tingling sensation.

Hazmat units aren’t sure what the substance is but said it did not contain hazardous or dangerous materials.

The person exposed to the material was evaluated while the school was placed on a brief lockdown.

Police are now tracing the source of the letter.