Families with children who go to Cornerstone Christian Academy in Ruthven are being asked to call the health unit after a student was diagnosed with the measles.
The Windsor Essex County Health Unit says the case has been confirmed by laboratory testing.
The exposure window was updated by the health unit on Wednesday afternoon to between February 21 and February 24.
Two additional points of exposure were also reported Wednesday afternoon. The first is at the TMC Kingsville Walk-In and Urgent Care clinic, on Saturday, March 1, from 9:20 a.m. to 12:15 p.m.
The second is at Windsor Regional Hospital's Met campus on Sunday, March 2, between 9:30 a.m. and 1:30 p.m., at the main entrance, elevators, and third-floor pediatric hallway.
For those who have not been vaccinated against measles or are immunocompromised, a post-exposure vaccination and assessment session will be held at the health unit on Wednesday evening from 5 p.m. to 8 p.m.
Those who have been exposed to measles may start to experience symptoms seven to 21 days after exposure.
Symptoms include a fever, runny nose, cough, drowsiness, irritability, red eyes, and a red rash on the face.
Anyone with those symptoms is urged to call their healthcare provider.
Measles is extremely contagious. The virus spreads easily in the air when an infected person coughs, talks, or sneezes. The particles can stay in the air up to two hours after the sick person leaves a closed space. It can also be spread by direct contact with secretions from the person's mouth or nose.