Health officials have confirmed the first case of measles in York Region as a Toronto-area mother took to social media to speak out against anti-vaccine activists after learning that her infant son was exposed to the virus.

Jennifer Hibben-White's son Griffin was exposed to the measles virus at a doctor's office in Markham, Ont. last month, she wrote in a Facebook post that has since been shared more than 186,000 times as of 8:30 a.m. Tuesday.

"I'm angry. Angry as hell," Hibben-White wrote in the Facebook post on Tuesday.

"I don't know if my baby will develop something that has death as a potential outcome. Death."

She wrote that she took her 15-day old son to the doctor's office for a newborn weigh-in appointment on Jan. 27. After she left, the doctor's office called her and advised her that someone who later developed measles was in the waiting room before their visit.

York Region Public Health officials confirmed Wednesday that there was one known case of the virus in the area north of Toronto. YRPH said that the man, who is younger than 30, had been vaccinated in the past.

There are six known cases of measles in the City of Toronto, four in adults and two in children. Toronto Public Health is still investigating whether there are any connections between the cases.

Though the person was in the waiting room sometime between half an hour and an hour before she and Griffin arrived, but measles is an airborne virus, and can stay on surfaces and in the air for up to two hours after the infected person had left.

Though she'd had the measles vaccine, her baby is too young to get his first dose.

Children are usually given a first dose of the measles-mumps-rubella vaccine at 12 months, and a second dose between the ages of 4 and 6.

Hibben-White also has a daughter, 3, who’s had only the first dose of the vaccination.

She wrote that she was told to keep the children in isolation and monitor them for symptoms of the virus (fever, cough or runny nose) for the next week. Though measles symptoms often mimic a cold or flu, the virus can also cause deafness and brain damage.

Measles has a 21-day incubation period, so Hibben-White will not know if they're in the clear until Feb. 17.

"I won't get angry at or blame the person in the waiting room. I would have likely done the same thing…you get sick, you go to the doctor. I have no idea what their story is and I will never know. But I do know one thing: If you have chosen to not vaccinate yourself or your child, I blame you."

Hibben-White directed her post at people who choose not to give children vaccines, believing they can cause harm. Those who speak out against vaccines, known as anti-vaxxers, have delayed getting their children vaccinated because they believe now-discredited research linking vaccines to autism and mercury poisoning caused by additives such as thimerosal.

" You think you are protecting them from autism? You aren't…" she wrote.

"You think you are protecting them through extracts and homeopathy and positive thoughts and Laws of Attraction and dancing by candlelight on a full moon? You aren't."

She asked rhetorically why her son had to bear the brunt of "reckless abuse," reiterating that she won't know if he's safe for another week.

"How's your week going, anti-vaxxers?"