Measles cases are accelerating, and in the last five months have caused more U.S. illnesses than in any entire year since 1996.
Health officials say 307 cases have been reported since New Year's Day. About half have been in the past month—most from a huge outbreak in unvaccinated Amish communities in Ohio.
That's a blistering start, even before the customary spurt of cases seen in the late spring and summer, health officials noted.
"Measles has reached a 20-year high. This is not the kind of record we want to break," said Dr. Anne Schuchat of the Centers for Disease Control and Prevention.
The CDC released the latest numbers Thursday during a news conference.
Nearly all the cases have been linked to travelers who caught the virus abroad and spread it in the United States among unvaccinated people. Many of the travelers had been to the Philippines, where a recent measles epidemic has caused more than 30,000 illnesses.
Most of the unvaccinated skipped shots for personal or philosophical reasons, Schuchat said.
About half of those who got sick have been adults 20 or older. At least 43 people were hospitalized with measles complications—mainly pneumonia. There have been no deaths.
No measles deaths have been reported in the U.S. since 2003.
The measles virus is highly contagious, spreading easily through the air and in closed rooms. Infected droplets can linger for up to two hours after the sick person leaves.
It causes a fever, runny nose, cough and a rash all over the body. In rare cases, measles can be deadly, and is particularly dangerous for children. Infection can also cause pregnant women to have a miscarriage or premature birth.
Before a vaccine became available about 50 years ago, nearly all children got measles by their 15th birthday—that's hundreds of thousands of cases annually. In those days, nearly 500 Americans died from measles each year.
According to CDC records, the last time the nation saw this many cases in an entire year was 1996, when 508 were reported.
The last time this many cases was reported this early in the year was 1994, when 764 cases occurred in the first five months. The end-of-year tally turned out to be 963.
Schuchat encouraged doctors to be on the lookout for measles, and urged the public to be fully vaccinated—especially before traveling overseas.