Most of the cases have been traced to outbreaks overseas and are mainly in children who were not vaccinated for religious or other reasons or were too young, 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.
Dr. Diana Yu, the Thurston County, Wash., public health officer, told the Olympian newspaper that eight members of a family developed symptoms of measles after attending a Generation Church Conference in Kirkland on March 25-29. None of the eight had been vaccinated against measles, Yu said.
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 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.
Thirteen of the U.S. cases were children younger than 1; children usually don't get their first measles shot until they're at least 1 because their immune systems are considered too immature to produce the needed response.
Such children can easily pick up infections from those around them, said Dr. William Schaffner, chairman of Vanderbilt University's department of preventive medicine.
"We have a responsibility not only to ourselves but to everyone around us" to get recommended vaccinations, he 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. 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.