ATLANTA — Measles cases in the U.S. are at the highest level in more than a decade, with nearly half of those involving children whose parents rejected vaccination, health officials reported yesterday.

Worried doctors are troubled by the trend fueled by unfounded fears that vaccines may cause autism. The number of measles cases is still small, just 131, but that's only for the first seven months of the year. Five of those cases were in Hawai'i.

There were only 42 cases in the U.S. for all of last year.

"We're seeing a lot more spread. That is concerning to us," said Dr. Jane Seward, of the Centers for Disease Control and Prevention.

Pediatricians are frustrated, saying they are having to spend more time convincing parents the shot is safe.

"This year, we certainly have had parents asking more questions," said Dr. Ari Brown, an Austin, Texas, physician who is a spokeswoman for the American Academy of Pediatrics.

The CDC's review found that a number of cases involved home-schooled children not required to get the vaccines. Others can avoid vaccination by seeking exemptions, such as for religious reasons.

Measles, best known for a red skin rash, is a potentially deadly, highly infectious virus that spreads through contact with a sneezing, coughing, infected person.

It is no longer endemic to the United States, but every year cases enter the country through foreign visitors or Americans returning from abroad. Measles epidemics have exploded in Israel, Switzerland and some other countries. But high U.S. childhood vaccination rates have prevented major outbreaks here.

In a typical year, only one outbreak occurs in the United States, infecting perhaps 10 to 20 people. So far this year through July 30 the country has seen seven outbreaks, including one in Illinois with 30 cases, said Seward, of the CDC's Division of Viral Diseases.

None of the 131 patients died, but 15 were hospitalized.

Childhood measles vaccination rates have stayed above 92 percent, according to 2006 data. However, the recent outbreaks suggest potential pockets of unvaccinated children are forming. Health officials worry that vaccination rates have begun to fall — something that won't show up in the data for a couple of years.

The vaccine is considered highly effective but not perfect; 11 of this year's cases had at least one dose of the vaccine.

Of this year's total, 122 were unvaccinated or had unknown vaccination status. Some were unvaccinated because the children were under age 1 — too young to get their first measles shot.

In 63 of those cases — almost all of them 19 or under — the patient or their parents refused the shots for philosophical or religious reasons, the CDC reported.

The nation once routinely saw hundreds of thousands of measles cases each year, and hundreds of deaths. But immunization campaigns were credited with dramatically reducing the numbers. The last time health officials saw this many cases was 1997, when 138 were reported.