The Virginia Department of Health this week said that stress was the culprit causing a mysterious "twitching" illness at William Byrd High School.

The mysterious illness, which caused odd "seizure-like" symptoms and affected about nine students and a staff member since the start of school in September, caused wide-spread panic at the Vinton, Va. school earlier this month.

Following a walkout by students and public outcry by parents and others, school officials hired outside experts who were assisted by the U.S. Centers for Disease Control and Prevention and state health officials to test the air, water and surface quality at the school. All tests came up clean.

After investigating the symptoms, health department officials determined that the people affected were not physically sick but were suffering from "mass sociogenic illness" also known as "mass psychogenic illness," the Roanoke Times reports.

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"The evidence is overwhelming that the vast majority of the illnesses were sociogenic in nature," a statement from the health department said.

A few people who live near the school told authorities they suffer from similar symptoms, but health officials say their conditions are unrelated to the symptoms inside the school.