The health unit has identified another possible measles exposure location in Windsor-Essex.
Those who were at Erie Shores HealthCare in Leamington at the emergency department between last Thursday night at 6:50 and just before 2 Friday morning should monitor themselves for symptoms for seven to 21 days.
The health unit reported earlier this week there are three confirmed cases of the highly contagious disease.
Officials expect more cases and exposure points in the coming days and weeks.