The worker, David Matthew Kwiatkowski, was charged with federal drug crimes. Authorities say the Michigan native stole drugs and contaminated needles while working at New Hampshire's Exeter Hospital Cardiac Catheterization Unit in 2011 and 2012.

Kwiatkowski allegedly injected himself with the painkiller Fentanyl intended for patients, and left the syringes for the hospital to re-use.

Hepatitis C is caused by a virus that attacks the liver, and is considered among the most serious hepatitis viruses. It is passed through contact with contaminated blood, often through shared needles.

Most people do not know they have the infection until liver damage shows up years or decades later. It can lead to cirrhosis or liver cancer.

Kwiatkowski is believed to have had hepatitis C since at least June 2010. Thirty cases of the same strain have been confirmed among patients from the New Hampshire hospital's cardiac catheterization lab.

New Hampshire health authorities are asking as many as 6,000 patients treated in the hospital's operating rooms and intensive care units between April 2011 and May 2012 to be urgently tested for possible exposure.

Before New Hampshire Kwiatkowski, 32, worked as a radiology technician and in cardiac labs in at least ten hospitals in Michigan, New York, Pennsylvania, Maryland, Kansas, Georgia, and possibly Arizona from 2007 to 2011.

A class-action lawsuit and separate negligence complaint were filed this week in U.S. District Court in Nebraska against Triage Staffing, a medical staffing agency that hired and placed Kwiatkoswki at Exeter Hospital.

(Reporting By Ros Krasny; Editing by Vicki Allen)

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