NEW YORK (AP) — Four people who were infected with a virus causing severe respiratory illness across the country have died, but what role the virus played in the deaths is unclear, health officials said Wednesday.

A 10-year-old Rhode Island girl died last week after suffering both a bacterial infection and infection from enterovirus 68, Rhode Island health officials said. The virus is behind a spike in harsh respiratory illnesses in children since early August.

The virus was also found in three other patients who died in September, according to the U.S. Centers for Disease Control and Prevention. The CDC declined to release any other details about those deaths.

It’s not clear what role the virus may have played in the four deaths, officials from Rhode Island and the CDC say.

The Rhode Island child’s death was the result of a bacterial infection, Staphylococcus aureus, that hit the girl in tandem with the virus, Rhode Island officials said in a statement.

They called it “a very rare combination,” and stressed that most people who catch the virus experience little more than a runny nose and low-grade fever.

The child was in good health before she developed severe breathing problems and her parents called 911, said Dr. Michael Fine, director of the Rhode Island Department of Health. She was taken by ambulance to a Providence hospital, where she died.

“Very quickly after they got to the hospital, things became dire,” Fine said at a news conference.

This enterovirus germ is not new. It was first identified in 1962 and has caused clusters of illness before. Because it’s not routinely tested for, it may have spread widely in previous years without being identified in people who just seemed to have a cold.

This year, the virus has gotten more attention because it has been linked to hundreds of severe illnesses. Beginning last month, hospitals in Kansas City, Missouri, and Chicago have received a flood of children with trouble breathing.

Some needed oxygen or more extreme care such as a breathing machine. Many, but not all, had asthma before the infection.

Health officials say they have not detected a recent mutation or other change in the virus that would cause it to become more dangerous.

The government says enterovirus 68 has sickened at least 500 people in 42 states and the District of Columbia. Almost all have been children.

Health officials are also investigating whether the virus played a role in a cluster of 10 Denver-area children who have suffered muscle weakness and paralysis.