The number of people with measles in Indiana this month has grown to 17 with a fresh case linked to an unvaccinated person who travelled to a country where the disease is prevalent, state health officials said on Monday.

Officials said they had confirmed the new case in Adams County in northeastern Indiana, but said it was unrelated to a rare outbreak of 16 cases that have been confirmed in central Indiana this month.

Measles, a highly contagious respiratory disease which in some cases can lead to hearing loss, pneumonia and death, is relatively rare in the United States due to high vaccination rates.

But last year saw the highest numbers in the United States since 1996, at 222 cases and 17 outbreaks, according to the U.S. Centers for Disease Control. One of the 2011 outbreaks also was in Indiana.

Dr. Jorge Parada, professor of medicine and direction of the infection prevention and control program at Loyola University Medical Center near Chicago, said the reason for the increased cases of measles in the U.S. was reduced rates of vaccination.

Transmission had occurred in Indiana this year in unvaccinated individuals or those with unknown vaccinated status, according to Indiana health department spokeswoman Amy Reel. According to the 2010 CDC National Immunization Survey, over 92 percent of Indiana children aged 19-35 months have at least one dose of the MMR or measles, mumps and rubella vaccine.

Two doses are required to attend school, though students have the option to provide proof of a religious or medical exemption.

The Adams County case has been traced to an unvaccinated person travelling to a country where measles is prevalent, according to the state health department. State and county Health Departments were investigating the new case to prevent further transmission.

While no longer infectious, officials warn that people who visited the Bluffton Regional Medical Center on February 20 may have been exposed to the disease when the measles sufferer went to the emergency room that evening.

People who were in the emergency room area that day may want to check their immunization records, officials said. Measles can also lead to pregnancy complications.

The cases in central Indiana included two people who visited the Super Bowl Village on February 3. No additional cases have been reported as a result of the Super Bowl Village exposure.

Three-quarters of all U.S. measles cases last year were transmitted locally, within the United States, rather than being picked up in another country. Two-thirds of people who avoid vaccination cite religious or philosophical reasons, Parada said.