Toronto's public health agency is investigating a measles outbreak of four cases, but officials are emphasizing the risk of infection is considered low.

Toronto Public Health is focusing on one person who may have exposed other people to measles by visiting Toronto East General Hospital, a community health centre and a Wal-Mart last week.

The health agency says the risk to the general public is low because most people are immune to measles as a result of past illness and Canada's high immunization rates.

Measles is highly contagious, but most people who get it are sick for about 10 days and recover completely without any treatment.

Symptoms include cough, runny nose, fever, white spots in the mouth, red watery eyes and a red rash.

Over the past five years there has been an average of 10 measles cases each year in Canada, with clusters of approximately four cases.

The last large outbreak happened in 2000 in Alberta and involved almost 200 people, most of whom were not immunized for religious or philosophical reasons. The original cases were imported from Mexico and Bolivia.