Boston ? The pasteurization process at a central Massachusetts dairy connected to a deadly outbreak of a bacterial illness appears to be working properly, a state health official said Friday.

Dr. Alfred DeMaria, the state director of communicable disease control, said that could mean the listeria bacteria that sickened four people in Massachusetts entered Whittier Farms’ milk supply after it was pasteurized. Two of those victims, a 78-year-old man and a 75-year-old man, died in June and October. Another elderly man and a pregnant woman survived, although the woman miscarried.

The Shrewsbury dairy has suspended operations and is cooperating with state officials trying to pinpoint the source of contamination, DeMaria said. The farm delivered milk mostly to homes in the Worcester area.

A message left for further comment was not immediately returned Friday.

DeMaria said the Massachusetts outbreak is believed to be just the third ever in pasteurized milk in the United States. Listeria is more commonly associated with luncheon meats, soft cheeses and hot dogs. It also can be found in raw, or unpasteurized, milk, he said.