Officials at the Children's Hospital of Philadelphia confirmed four cases of Enterovirus D68 (EV-D68) among their patients.

CHOP officials say they received results of testing by the Centers for Disease Control of five samples from patients with symptoms consistent with a respiratory virus. After analyzing the samples, they confirmed four as EV-D68. They also say the fifth was caused by a different strain of respiratory virus.

"All of these patients have recovered and have been discharged from the hospital after inpatient stays that ranged from 2 to 6 days," a CHOP spokesperson wrote in an official statement.

The Pennsylvania Department of Health also announced Tuesday three confirmed cases of EV-D68 in Pennsylvania residents.

“The department is working with the Philadelphia Department of Public Health on this particular cluster and will continue to monitor the situation closely statewide, as we have been since cases have increased rapidly across the country in recent weeks,” said Physician General Dr. Carrie DeLone. “Parents should be vigilant and aware of signs and symptoms, but it’s also important to know that there are other respiratory illnesses that are circulating and the best course of action if you’re unsure is to talk with your healthcare provider.”

Pennsylvania is one of 12 states with confirmed cases of Enterovirus 68. Centers for Disease Control and Prevention officials say Pennsylvania, Alabama, Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Missouri, New York, and Oklahoma together have 130 lab-confirmed cases. All are children.

The virus can cause mild to severe illness, with the worst cases needing life support for breathing difficulties. Kids with asthma have been especially vulnerable. No deaths have been reported. Symptoms of the virus include fever, runny nose, mouth blisters and muscle aches.

The strain is not new but only a small number of labs can test for it. Since mid-August, there's been an unusual spike in identified cases. The CDC has tested more than 200 specimens from more than 30 states.

Investigators say it's not yet clear what triggered the outbreak or whether it's worsening.

Anyone with respiratory illness should contact their doctor if they are having difficulty breathing or If their symptoms are getting worse. There is no specific treatment for EV-D68 but experts say you can protect yourself from the illness by doing the following: