Eight years after it was declared practically dead in the U.S., measles is making a comeback.

Outbreaks of the highly contagious virus in nearly a dozen states have led to more than 70 cases this year, federal health officials said Thursday.

Those are the highest numbers in six years.

The hardest hit area has been New York City, where 22 cases of measles have been recorded.

"We're still investigating where some of these cases may have come from," said Dr. Christopher Zimmerman, the director of epidemiology and surveillance for New York City's health department.

"But, we believe all of them are related to international travel."

The Centers for Disease Control and Prevention has come to similar conclusions.

In a statement, the CDC said most of the cases have been traced to outbreaks overseas and most of the victims have been children who were not vaccinated.

"The difference we are seeing right now is there is much more back-and-forth travel between Europe and New York and Israel and New York," said Zimmerman.

Of the 22 cases, some involved U.S. citizens traveling to Belgium and others involved people traveling from Israel to New York.

"If you're traveling to Europe or Israel, make sure you're up to date with all your routine immunizations," said Zimmerman.

And if you have guests coming to visit from overseas — the same rules apply to them.

"Make sure your visitors are up to date with their vaccinations as well, so they don't bring the virus over here," he added.

So far this year the CDC has confirmed reports of 64 cases of measles in nine states. There have been no deaths, but 14 people have been hospitalized, said CDC spokesman Curtis Allen.

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That count doesn't include Washington state, where eight cases were reported this week. Those cases stemmed from an international church conference in suburban Seattle in March, according to the state health department.

Measles is caused by a virus that normally grows in cells that line the back of the throat and the lungs.

"It’s actually one of the most communicable infectious diseases in the world," said Dr. Joseph Rahimian, an infectious disease specialist at St. Vincent's Hospital in Manhattan.

Typical symptoms include:

— Coughing

— Runny nose

— High Fever

— Rash (which usually starts on the face and spreads to the rest of the body)

About 1 in 5 measles sufferers experiences more severe illness, which can include diarrhea, ear infections, pneumonia, encephalitis, chronic neurological deficits and even death.

Of the 64 cases reported to the CDC as of last week, 63 were unvaccinated or it wasn't known if they were vaccinated. At least 54 of the cases stemmed from outbreaks in Switzerland, Israel or other countries, Allen said.

"I think there are a couple factors leading to this outbreak," said Rahimian.

"What concerns me is the trend of more and more people not vaccinating their children because of fears that vaccines cause autism — although no studies have proven this to be true."

Another issue is immigrant health.

"These two factors combined could cause this to be a much bigger epidemic," he said. "But, as long as we stay vigilant... a few cases can be managed."

Arizona, California, Michigan, Wisconsin, Hawaii, Illinois, Pennsylvania and Virginia have also reported cases of measles.

It's the largest number of cases since 2001, when 116 cases were documented. Officials expect this year's tally to keep climbing past that mark, said Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases.

The worst year for measles was 1958, according to modern public health records. More than 763,000 cases were reported that year, including 552 deaths. Outbreaks in the early 1990s led to a revision of vaccination guidelines to include children younger than school age.

Since measles vaccinations began in the early 1960s, cases have dramatically declined in the U.S.

If you're concerned that you are not up to date with your measles vaccinations, check with your primary care physician. All it takes is a simple blood test.

Click here for more information on the outbreaks from the CDC

The Associated Press contributed to this story.