WASHINGTON — A serious respiratory illness sickening U.S. children has spread to 12 states, the Centers for Disease Control and Prevention said on Tuesday, as it predicted that more states will report cases in coming weeks.

The growing list of states with confirmed cases now includes Alabama, Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Missouri, New York, Oklahoma and Pennsylvania, the CDC said.

Known as enterovirus D68, the somewhat rare virus can cause symptoms ranging from mild fevers to difficulty breathing and wheezing severe enough to require hospitalization.

Since mid-August, the CDC has received reports of 130 people with confirmed cases of the virus. There is no vaccine and infants, children and teenagers have the greatest risk of infection. So far, there have been no reported deaths from the illness, which could be fatal in serious cases.

Many of the children who became very ill in Missouri and Illinois, where early outbreaks were seen, had asthma or a history of wheezing, said the CDC, which is working with state health officials to better understand infection trends.

U.S. health officials expect more states to confirm cases in the weeks ahead, noting that clusters of illness are under investigation in several states and that testing to confirm the virus takes time.

More reported cases may just mean a testing backlog is clearing, and not necessarily that the situation is worsening, CDC said.

On Monday, the Alabama Department of Public Health said it was investigating reports of children suspected to have contracted the virus and had confirmed several cases in the southern part of the state.

Over the weekend, the Connecticut Department of Public Health said it had received reports of young children with severe illness from two hospitals in different parts of the state that could be due to the virus.

To limit the spread of the illness, public health officials have urged frequent hand washing and encouraged asthma patients to take their medications and try to control their illness.

The summer and fall are prime seasons for enteroviruses to spread in the United States, according to the CDC, and health officials expect infections of the strain to taper off later this year.