A San Francisco Costco has recalled 39,755 lbs. of Foster Farms rotisserie chicken products after at least one person was sickened by Salmonella Heidelberg, the foodborne pathogen that has sickened 317 people in a 20-state outbreak, according to the U.S. Department of Agriculture’s (USDA) Food Safety and Inspection Service (FSIS).

FSIS investigators discovered possible contamination in Kirkland Signature Foster Farms rotisserie chickens, Kirkland Farm rotisserie chicken soup, leg quarters, and chicken salad sold between Sept. 11 and Sept. 23 at the Costco on 1600 El Camino Real.

It’s still unclear how the Costco chicken caused illness in one victim because all Costco chicken is cooked to at least 180°F, Craig Wilson, the wholesale store’s vice president for food safety, told the Los Angeles Times. “It was well-cooked,” he said. This particular Costco roasts 1,000 chickens a day — much more in comparison to other stores. “It may have been a very, very uncommon cross-contamination issue,” Wilson said. “We’re still researching.”

The Centers for Disease Control and Prevention (CDC) says that chicken should be cooked to a temperature of at least 165°F in order to kill any foodborne bacteria. In a statement, the FSIS reminded consumers that following the package’s instructions with regards to cooking time doesn’t mean that the chicken is cooked, and that a thermometer should be used to check internal temperature.

Costco is the second major retailer to recall Foster Farms chicken. Kroger Co. pulled chicken from the three Foster Farms processing plants off its shelves last week. Even with the severity of the outbreak, the USDA and Foster Farms did not issue a recall of all of the chicken in question because they consider Salmonella to be a naturally occurring bacterium that can be killed by cooking the food thoroughly. 

The USDA nearly closed the three Foster Farms facilities — two in Fresno and one in Livingston, Calif. — last week, but chose not to after the chicken company revealed plans to clean up areas where contamination was likely.

Salmonella Heidelberg, however, has already caused double the hospitalizations than expected for an outbreak of its size. The particular strain has been found to be resistant to multiple types of antibiotics. As of Oct. 11, 42 percent of those sickened were hospitalized, and 13 percent of them had Salmonella septicemia, a life-threatening full-body inflammation caused by infection of the blood.

To prevent illness from Salmonella and any kind of cross-contamination, here are six tips for buying, washing, and cooking chicken safely