MESA, Ariz. >> Patients at a health center in Mesa were exposed to a measles outbreak that originated at California’s Disney parks nine days before the first alerts to the public, health officials have confirmed.

Health officials said they did not disclose the Jan. 11 exposure, involving a visit by a Pinal County measles patient to Phoenix Children’s Hospital’s East Valley Center, because they thought the exposure was small enough to contain without alarming the public, the Arizona Republic reports.

Officials said 18 people were exposed at that time.

The first alert regarding the center was issued on Tuesday, after a Maricopa County measles patient possibly exposed 195 people Jan. 20-21 at the same health center. Officials now say as many as 1,000 people in three counties could have been exposed.

Because fewer people were exposed Jan. 11, officials thought it was “more likely to be contained and we could track exposed individuals more easily,” said Jeanene Fowler, a spokeswoman for the Maricopa County Public Health Department.

Arizona is second to California in the number of cases traced to visits to Disney parks last month. Measles has been confirmed in five other states — Utah, Washington, Colorado, Oregon and Nebraska — and Mexico. Most of those infected were not vaccinated, and health officials have urged people to get the measles shot.

Those in Arizona who were possibly exposed are being contacted by Maricopa County and Phoenix Children’s, which is connected to the Mesa center.

Patient contacts regarding the Jan. 11 exposure are being handled by Phoenix Children’s, spokeswoman Jane Walton said. “Staff immediately began contacting those families by phone with follow-up by certified mail,” she said.

On ABC’s “This Week,” Arizona Gov. Doug Ducey was asked if there were any extra measures being taken at the Super Bowl because of the measles outbreak.

“We’re working with our health services here in Arizona, both county and local,” the Republican said. “And like I said, we’re working also with all the law enforcement agencies so that we make sure people are safe. But we’re monitoring that situation, and we’re on the case.”