(HealthDay)—A rare, polio-like condition in children is on the rise again in the United States, with 38 confirmed cases in 16 states so far this year, the U.S. Centers for Disease Control and Prevention says.

The condition, acute flaccid myelitis, was first identified in 2014, when there were 120 , NBC News reported. The condition has been linked to viruses, including EV-A71, a common cause of hand, foot, and mouth disease.

The CDC says the number of cases appears to increase and decrease from one year to the next. After the 120 cases in 2014, there were 22 in 2015, 149 in 2016, and 33 last year, according to the agency.

Of the 38 reported cases so far this year, 14 have been in Colorado and six are under investigation in Minnesota, NBC News reported.