The southwestern Ontario rubella virus outbreak likely originated in the Netherlands, Ontario's chief medical officer of health says.

"We are speculating that it was introduced from the Netherlands, given the cross-border traffic that exists between this community and a similar community in the Netherlands," Dr. Sheela Basrur said Monday of the cluster of religious communities in Ontario.

"They've had an outbreak going on for eight months now in what they call the Bible Belt."

Health officials said the outbreak has grown to include 121 confirmed cases and could drag on for some weeks yet.

"We're really still in the phase of the outbreak where our investigations will lead to more people (with the virus)," said provincial Health Minister George Smitherman.

"We're not at a point yet where we can declare the outbreak under control."

At the heart of the outbreak is Rehoboth Christian School, in the rural community of Norwich, where approximately 60 per cent of students were never vaccinated against the virus due to religious concerns.

Other cases were subsequently reported in the neighbouring Oxford, Haldimand-Norfolk and Brant counties.

In a statement Sunday, health officials confirmed there is now a possibility the outbreak has spread to the heavily-populated Middlesex-London area. The new concern stems from the recent diagnosis of a 32-year-old already-vaccinated Norwich man who attends Westervelt College in London.

"All students and staff at Westervelt College will be asked to check their immunization status for rubella, report any symptoms of rubella, and stay away from others if symptoms should appear," medical officer of health Dr. Graham Pollett said in a statement.

It is believed the man became infected after coming in contact with fellow students who are siblings of children attending the Rehoboth Christian School.

Basrur said there is no evidence that the virus has moved into other nearby religious groups. Still, she will be urging the children of all religious groups to ensure their children are vaccinated.

"We have not yet seen spread to the Amish or Mennonite communities. (But) they do live in adjacent geographic areas. And so for that reason, those health units in which they live will be redoubling their efforts to encourage them to seek vaccination," she said.

Rubella, also known as German measles, is a viral illness spread through coughing or sneezing. Although highly contagious, the typical symptoms are considered mild.

While children usually suffer a mild rash, adults can be harder hit by more severe complications. The spectrum of symptoms includes fever, headaches, joint pain and runny noses.

The greatest risk, however, is posed to pregnant women and their fetus.

The disease cannot only increase the chance of a miscarriage, it can also lead to babies born deaf or blind, with cognitive disabilities or damaged hearts.

Health officials recommend that anyone who has not had a rubella vaccine should get one.

With files from The Canadian Press