Public health officials said they are now dealing with a measles outbreak in southwestern Ontario, with 19 confirmed cases as of Jan. 29.

Southwestern Public Health, which covers Oxford County, Elgin County and the City of St. Thomas, is reporting three cases of the highly contagious disease in children.

The remaining 16 infections are with Grand Erie Public Health, which serves the City of Brantford, Brant County, Haldimand County and Norfolk County. In an update Friday, officials said thirteen children and three adults have measles.

“When this started, we were looking at this being just a cluster of cases that were occurring predominantly in a non-immunized group,” explained Dr. Malcolm Lock, the acting medical officer of health for Grand Erie Public Health. “We’ve now moved to calling it an outbreak because of the numbers that are very rapidly increasing and the numbers that we think are going to continue to increase.”