New York City Mayor Bill de Blasio speaks during a news conference declaring a public health emergency in parts of Brooklyn in response to a measles outbreak, requiring unvaccinated people living in the affected areas to get the vaccine or face fines, in the Orthodox Jewish community of the Williamsburg neighborhood, in Brooklyn, New York City, April 9, 2019.

Another 90 measles cases were reported in the U.S. last week, putting 2019 on track to be the worst year for the disease since public health officials said it was eradicated in 2010, according to the latest data from the Centers for Disease Control and Prevention.

The CDC has confirmed 555 measles cases from Jan. 1 through April 11 — approaching the 667 cases diagnosed in 2014 — just four months into this year.

Of the 90 new cases reported last week, 77 were in New York, the CDC said. Fifty cases were reported in New York City and 27 were reported in Rockland County. New York City Mayor Bill de Blasio last week declared measles a public health emergency and ordered mandatory vaccinations for people living in Brooklyn's Williamsburg neighborhood where the disease is spreading.

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Since January, the disease has been reported in 20 states. Outbreaks, defined as three or more cases, are ongoing in five areas: New York City, New York State's Rockland County, Washington, New Jersey, California's Santa Cruz County and California's Butte County.

The CDC said travelers brought back the disease from places like Israel and Ukraine where large measles outbreaks are occurring. Worldwide, there has been a 300% increase in measles cases, to about 112,000 in the first three months of the year from about 28,000 at the same time last year, the World Health Organization said Monday, citing preliminary data.

Measles is highly contagious, infecting up to 90 percent of unvaccinated people who are exposed to it, according to the Centers for Disease Control and Prevention. The virus can live in the air for up to two hours after an infected person coughs or sneezes, according to the CDC, meaning people can be exposed to it without ever knowing.

People can be infected for days before showing signs of the virus, such as a fever, runny nose or a rash.