Local and state health officials are investigating the outbreak that has sickened at least 38 inmates, prison spokeswoman Lori Scamahorn said Wednesday.
The illness sent 17 to the hospital and another 21 suffered similar but less severe symptoms, Scamahorn said.
Four staff members also were sick, but it was not clear if their illnesses were related.
Most of the sick inmates are from the segregation units, where they eat from trays alone in their cells. So far, six have tested positive for campylobacter jejuni.
Campylobacter is a communicable disease that can cause bloody diarrhea, abdominal pain, fever, cramping, nausea and vomiting. In healthy people it usually resolves itself within a few days. It can be serious, although rarely fatal, in people with other significant health problems.
All of the people diagnosed with the disease are being treated with antibiotics.
In March, 65 inmates became ill with campylobacter.
A recent Washington state Department of Health report on the earlier outbreak concluded the contamination of a stainless steel food preparation table was the culprit.
The penitentiary changed food preparation practices after that incident, including stressing hand-washing among inmates, requiring food handlers to wear gloves during preparation and serving, and thoroughly sanitizing food preparation surfaces.
It appears that not all of those measures are being followed correctly, Scamahorn said.