INDIANAPOLIS — East Coast fans who left the Super Bowl host city feeling good about Hoosier hospitality may have been exposed to something less welcome: The measles.

On Wednesday, the Indiana State Department of Health alerted public health officials in Massachusetts and New York that some of their residents may have come in contact with the rare but highly contagious measles virus when visiting the crowded Super Bowl Village in downtown Indianapolis.

Indiana health officials reported four cases of the measles Wednesday, including one infected person who was at the open-air Super Bowl festival site last Friday during the afternoon and evening hours, when an estimated 200,000 people were in close proximity to one another.

Among those in the Friday crowd were New Yorkers and New Englanders who traveled to Indianapolis before last Sunday’s game. Many arrived early because many Indianapolis hotels catering to the Super Bowl crowd required a four-night minimum stay.

Indiana Health Commissioner Dr. Gregory Larkin said chances are “extremely low” that anyone in the crowd would have been infected by the airborne virus, but said state health officials had to err on the side of caution.

“We’re required to report even one case,” Larkin said of federal health rules aimed at containing the once-common and now-rare virus that can be serious or even fatal to young children and dangerous for pregnant women.

The measles virus is spread when an infected person sneezes or coughs, spraying droplets of the virus that remains active and contagious on an infected surface for up to two hours. Early symptoms can mimic a cold.

Larkin said most people in the U.S. have been vaccinated against measles, which reduces its transmission levels. He also said the odds of the virus spreading quickly in an open-air site are much lower than indoors.

He said the infected person didn’t go into the NFL Experience, an indoor theme park set up inside the Indiana Convention Center and visited by 25,000 people Friday.

The measles alert came just days after fans of the New York Giants and New England Patriots left Indianapolis singing the city’s praises. Many of those fans, along with national media and NFL officials, issued public statements and posted messages on Twitter and Facebook praising the city’s ability to pull off the Super Bowl spectacle without a hitch.

Larkin said the fast reporting of the four measles cases will make it easier to contain the spread of the disease.

Larkin said federal privacy laws prohibit the release of the identity of the infected person who visited the Super Bowl Village. Larkin said the person  likely didn’t know he or she was infected because the early symptoms can be mild: a runny nose or cough that escalates to a high fever before the outbreak of a rash.

State health officials confirmed two cases of measles in Hamilton County, just north of Indianapolis, and an additional two probable measles cases in nearby Boone County.

Indiana health officials were urging parents in those counties to contact their children’s doctors to check immunization records. They also encouraged anyone who was in the Super Bowl Village area between 3 and 10 p.m. last Friday to do likewise.

Vaccination is the most effective way to prevent transmission. Health officials said more than 95 percent of people who receive a single dose of the measles vaccination will develop immunity and more than 99 percent will be protected after receiving a second dose. Individuals born before 1957, when the measles virus was more common,  are presumed to be immune.

Maureen Hayden covers the Statehouse for the CNHI newspapers in Indiana. She can be reached at maureen.hayden@indianamediagroup.com