EXETER, N.H. —  New Hampshire’s Exeter Hospital has temporarily closed its cardiac catheterization lab after four patients contracted hepatitis C, and officials are asking 651 other people who’ve been treated at the lab since August to get tested for the liver-destroying virus.

Dr. Jose Montero, the state public health director, said the investigation began in mid-May when some of the patients became ill.

All four were diagnosed with an identical strain of the virus, and the only link officials could find was that they all had been treated at the lab.

Officials haven’t determined how the four individuals contracted the virus, which is most commonly spread through sharing needles to inject drugs.