A rare but serious viral infection continues to send children to hospitals across the U.S., and the number of states with confirmed cases is growing. Officials in both Alabama and New York announced recently that they have received confirmation that suspected cases of enterovirus D68 are authentic.

Four of six specimens tested in Alabama were positive, according to an announcement on Monday by the state’s Department of Public Health. Last Friday, The New York State Department of Health stated that more than a dozen children in two separate parts of the state have confirmed enterovirus D68 illnesses.

The confirmation of cases in Alabama brings the total number of states with enterovirus D68 infections to ten. Connecticut and several other additional states that rely on specimen-testing provided by the U.S. Centers for Disease Control and Prevention are awaiting confirmation of suspected cases. New York is one of the few states that have the capacity to test for the virus within its borders.

Enterovirus D68 is one particularly rare members of the many non-polio enteroviruses, some of which cause illnesses with cold-like symptoms. Enterovirus D68 was first isolated in 1962 in California and has only occasionally caused noticeable outbreaks to date. The virus causes mild to severe respiratory illness and symptoms such as coughing, sneezing, and in some cases, difficulty in breathing.

So far, enterovirus D68 has only caused respiratory illness in children. Experts say that nearly all adults have been exposed to the viral strain at some earlier point in their lives. Therefore, they have already established immunities to this particular strain. The children who are becoming ill, however, have not experienced this virus before and do not have established immunity against it.

Last week, health officials in the Denver, Colorado, area reported hundreds of new cases. There are no specific treatments or vaccines against enterovirus D68.