(CNN) A total of 387 individual cases of measles have been confirmed in 15 states from January 1 to March 28, according to the US Centers for Disease Control and Prevention. This is the second-greatest number of cases reported in the United States since measles was declared eliminated in 2000. The highest number of reported cases since elimination was 667 in 2014.

Measles is a highly contagious disease caused by a virus that can spread through the air when an infected person coughs or sneezes, or if a person comes into direct contact or shares germs by touching the same objects or surfaces.

The states reporting cases are Arizona, California, Colorado, Connecticut, Georgia, Illinois, Kentucky, Michigan, Missouri, New Hampshire, New Jersey, New York, Oregon, Texas and Washington.

The CDC says six outbreaks -- defined as three or more cases -- are ongoing in California (Santa Cruz and Butte County), New Jersey, New York (Rockland County and New York City) and Washington.

These outbreaks are linked to travelers who brought measles back from other countries such as Israel, Ukraine and the Philippines, where large measles outbreaks are occurring.

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