A former temporary worker at Exeter Hospital in New Hampshire was arrested yesterday in relation to a hepatitis C outbreak that infected 30 patients, the FBI reported.

The worker, David Matthew Kwiatkowski, 32, allegedly took syringes containing the drug Fentanyl, injected himself, then refilled the syringe with another liquid, according to the FBI. Fentanyl is an anesthetic and a controlled substance.

Kwiatkowski is suspected of infecting others with hepatitis C after they received fluid from tainted syringes, according to the FBI. Testing of blood samples from Exeter Hospital patients showed genetic similarities between Kwiatkowski’s hepatitis C strain and that which infected 30 patients.

Exeter Hospital said Kwiatkowski began working at the facility in April 2011 as a temporary employee.

“As with all travelers at Exeter Hospital, pre-employment drug testing and standard and criminal background checks were performed,” the hospital said in a statement. “He was hired into a regular full-time position as a cardiovascular tech in our cardiac catheterization lab in October of 2011, where he worked until he was placed on leave at the onset of the investigation in May, and then was later terminated.”

Exeter Hospital said it can’t comment on the case because of the ongoing criminal investigation as well as because Kwiatkowski is both a former employee and a former patient.

The FBI reported Kwiatkowski was seen leaving the cardiac catheterization lab during procedures, sweating profusely, attending procedures on his off days and engaging in other suspicious behavior. The agency also reported that investigators found an empty Fentanyl syringe and several needles in his vehicle.

Kwiatkowski told law enforcement that he only learned he had hepatitis C in May 2012, but investigators found evidence that he had the disease since at least June 2010, according to the FBI.

The U.S. Attorney’s Office is working with other states where Kwiatkowski worked to uncover any problems. Kwiatkowski is originally from Michigan but worked as a traveler in at least six states before coming to New Hampshire, according to the FBI.

Hepatitis C is a blood-borne virus that causes serious damage to the liver.