Two Toronto school boards sent letters home with students on Friday, in response to an ongoing measles outbreak that has infected six people in the city.

On Friday, Toronto Public Health confirmed that another adult had contracted the measles virus, bringing the total number of known cases to four adults and two children.

TPH spokesperson Lenore Bromley says the latest person to become infected was born before 1970, before the measles vaccine was introduced in Canada. A woman in the Niagara region has also contracted the disease.

One of the six infected people in Toronto was a patient at St. Joseph's Health Centre.

In a statement released on Friday, St. Joseph’s said a patient who was in the hospital’s emergency department from Jan. 27 to Jan. 29 has been diagnosed with measles.

Hospital officials worked with TPH to ensure that those potentially exposed to that patient were notified.

"At this time St. Joseph's has no confirmed measles cases in our facility," the hospital said.

The hospital is not releasing the name of the infected individual due to patient confidentially.

TPH says it is still investigating whether there are any connections among the cases in Toronto.

TPH has asked the Toronto District and Toronto Catholic District school boards to send a letter home with students that provides more information on the virus and vaccinations.

The letter tells parents that if there is a measles exposure at a Toronto school, those without vaccinations will not be allowed to attend the school until the outbreak is over.

With files from The Canadian Press