U.S. health officials have reported that 2011 has had the highest rate of measles since 1996, with 118 cases in the United States so far.

The Centers for Disease Control and Prevention on Tuesday released the count for January 1 through May 20. Cases were seen in 23 states. None of the patients died, but about 40 percent were hospitalized.

The U.S. normally sees about 50 cases of measles in a year, thanks to vaccinations. About 90 percent of the cases this year were unvaccinated.

Measles is highly contagious and up to 90 percent of people exposed to an infected person get sick. The virus spreads easily through the air, and in closed rooms, infected droplets can linger for up to two hours.

The Associated Press contributed to this report.