WASHINGTON, May 13 (Xinhua) -- At least 839 measles cases have been confirmed in 23 states of the United States as of May 10 since the beginning of this year, the U.S. Centers for Disease Control and Prevention (CDC) reported on Monday.

A total of 75 new cases were reported in the week ending May 10, among which 41 were reported in New York City and 25 in nearby Rockland County.

Measles is a virus that causes fever and rash. It is highly contagious and anyone who is not vaccinated against the virus can get it at any age.

The New York City Department of Health and Mental Hygiene has declared a state of emergency and ordered residents of a neighborhood in Brooklyn to get the vaccine or face a 1,000 U.S. dollar fine.

Experts believe the resurgence of measles cases in the United States is due to reintroduction by international travelers from countries experiencing measles outbreaks, coupled with low vaccination rates in certain localities.