A measles outbreak in southwestern Ontario continues to grow, with three more confirmed cases announced on Friday.

The latest patients are children in Norfolk County, part of Grand Erie Public Health, which also oversees Haldimand, Brant and Brantford.

Grand Erie now has 19 confirmed measles cases this year and all but three are in children.

The health unit said one child was hospitalized but has since been released.

The rapidly rising case count prompted Grand Erie鈥檚 acting medical officer of health, Dr. Malcolm Lock, to declare a measles outbreak on Wednesday.

While announcing the latest confirmed measles cases, the health unit said people who visited Walsingham Christian School on Jan. 20 or 21, Houghton Public School on Jan. 21 or LaSalette Old Colony School on Jan. 21, 22 or 24 may have been exposed to the highly contagious disease. It spreads by droplets that can hang in the air for several hours after an infected person leaves the area.

A spokesperson for the Grand Erie District School Board directed The Spectator to the health unit and said staff at the public school board 鈥渨ork collaboratively in these matters and rely on their expertise.鈥�

Residents may have also been exposed at the Delhi walk-in clinic the night of Jan. 23, Langton Arena the afternoon of Jan. 25 and the emergency departments at Woodstock General Hospital and Norfolk General Hospital in Simcoe in the morning and early afternoon of Jan. 27.

The emergency department at Tillsonburg District Memorial Hospital is another potential exposure site. The health unit advises visitors on Jan. 25 from 9 a.m. to 1 p.m., and Jan. 26 from 10:37 p.m. to 12:45 a.m., to monitor for measles symptoms, which can take up to two weeks to show themselves.

The main symptoms are fever, red rash, runny nose, cough, red eyes and fatigue. More severe outcomes are possible in people born after 1970 who are not double-vaccinated against measles, mumps and rubella (MMR).

Lock said it is 鈥減redominantly鈥� unvaccinated people or those with only one dose who are catching the measles in Norfolk and across Ontario.

鈥淚 can鈥檛 emphasize more the contagiousness of this disease and the fact that we should take as many precautions as we can,鈥� said Lock.

He assured residents the MMR vaccine is safe and two doses provide nearly 100 per cent protection.

鈥淲e would encourage people, especially in the area where these cases are occurring, that they should check their vaccination records and make sure they鈥檝e had their two doses,鈥� Lock said.

The Norfolk cases have an effect on neighbouring health units, since some west-end residents use hospitals governed by Southwestern Public Health.

Dr. Ninh Tran, Southwestern鈥檚 medical officer of health, said his health unit has three lab-confirmed measles cases in local children but a 鈥渟ignificant number of exposures鈥� due to residents travelling between his region and Haldimand-Norfolk.

Lock and Tran urged anyone with possible measles symptoms to call ahead before visiting a clinic, doctor鈥檚 office or hospital in order to reduce the risk of exposing others to the virus.