EXETER — The cardiac catheterization lab at Exeter Hospital reopened Friday afternoon after the state Department of Public Health determined that it was safe to resume operations for emergencies following a hepatitis scare, the hospital said.

The announcement came a day after state health officials and the hospital confirmed that four people who were patients in the lab were diagnosed with the identical strain of hepatitis C, a blood-borne illness that can lead to liver problems.

The lab closed on May 25 as an investigation began into the hepatitis cases that officials said appear to be linked to the lab and its recovery unit.

The hospital is contacting more than 650 patients who received care through the lab between August 2011 and May of this year and asking them to be tested for possible hepatitis C. Officials have not pinpointed the cause of the outbreak, which is the first of its kind at a medical facility in New Hampshire.

“After thoroughly examining Exeter Hospital's cardiac cath lab, the New Hampshire Department of Public Health has informed Exeter Hospital that the cardiac cath lab is safe to resume operations on an emergency services basis. We believe it is vitally important to share that the cardiac cath lab has reopened as of 4 p.m. on Friday for emergency care and is expected to return to normal operations early next week,” the hospital said in a press release.

The hospital said it will continue to work closely with state health officials and is doing its best to accommodate and to support its patients during the process.

“We have contacted and sent a letter to all of the patients identified for testing and as of 4 p.m. (Friday), approximately 400 patients have been screened or have made an appointment. We will continue to take phone calls and schedule appointments with all of the identified patients until they are tested. This is an evolving situation and we will continue to share more information as it becomes available,” the hospital said.

Those with questions are urged to call the New Hampshire Division of Public Health at 271-4496 or Exeter Hospital's Information and Referral Center at 580-6124.