Measles is a respiratory disease caused by a virus, that spreads through breathing, coughing and sneezing. While measles is harder to come by in the United States, the CDC notes it's still a worldwide public health problem that can be brought over to the country and spread to Americans. One CDC expert pointed out that a measles infection can linger for four hours even after the infected person is no longer in the vicinity.

"Clusters of people with like-minded beliefs leading them to forgo vaccines can leave them susceptible to outbreaks when measles is imported from elsewhere," Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases, told reporters Thursday during a teleconference. "This is an extraordinarily contagious virus."

Such clusters included people with similar religions, those with extended large extended families or even certain school districts where vaccine rates are low.

So far this year, 159 cases of measles were reported in 16 states, with three outbreaks accounting for most of cases: outbreaks in New York City (58 cases), North Carolina (23 cases) and Texas (21 cases). That's on track for the most cases since measles was considered eliminated.

Fortunately, said Schuchat, nobody has died.

Eighty-two percent of cases were in unvaccinated persons, and 9 percent were in people who weren't sure if they'd been vaccinated. Seventy-nine percent of those the unvaccinated cited philosophical differences with the measles mumps and rubella (MMR) shot.

The CDC said recent misinformation about the measles vaccine -- including asince-disputed link to developing autism from vaccines -- may still be influencing some families. Schuchat called on pediatricians and doctors who have close relationships with these families to convince them otherwise.

In recent years, some pediatricians have even fired patients if parents won't get their kids vaccinated, citing risks of infecting other kidsin their practices.

The new measles report coincides with a CDC release of a national report card of vaccines in infants aged 19 to 35 months. This year marks the 20th anniversary of legislation that created the Vaccines For Children Program, a federally-funded effort to provide no-cost vaccines to kids whose families can't pay.

The program was first launched to combat a national measles crisis in the late 1980s, Schuchat explained, when a vaccination gap was evident in preschoolers who would get turned away from pediatricians because parents could not afford shots, only to be referred to a community health clinic where the families might not show up.