ATLANTA (AP) -- Measles outbreaks in several states have led to more than 70 cases so far this year, the worst in six years, health officials said Thursday.

Most of the cases have been traced to outbreaks overseas and are mainly in children who were not vaccinated for religious or other reasons, according to the Centers for Disease control and Prevention. Since measles vaccinations began in the early 1960s, cases have dramatically declined in the U.S.

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

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 line the lungs. It spreads through contact with a sneezing, coughing, infected person.

Symptoms include rash, high fever, cough, runny nose, and red, watery eyes. But about 1 in 5 measles sufferers experience more severe illness that can include diarrhea, ear infections, pneumonia, encephalitis and even seizures and death.

Of the 64 cases reported to the CDC, 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.

The largest concentration has been in New York City, with 22 cases. Arizona has had 15, California, 12, and Michigan and Wisconsin have each had four. Hawaii, Illinois, Pennsylvania, Virginia and upstate New York also reported cases.

It's the largest number of cases since 2001 when 116 cases were reported, according to CDC records.

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.

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