The Washington Department of Health (DOH), the Tacoma-Pierce County Health Department, and Thurston County Public Health and Social Services investigated an outbreak of Listeria monocytogenes in July and August 2023. Six cases of listeriosis were reported by August 9, 2023. This cluster was given the outbreak code 2306WAGX6-1.

Cases ranged from 43 to 79 years (median 63.5). Sixty percent (60%) were male. Five of the six cases had serious underlying health conditions, which put them at high risk for Listeria infection. All six were hospitalized, and three out of these six cases have died. Illnesses ranged from February 27 to July 22, 2023. These cases were residents of Pierce (5) and Thurston (1) County.

Whole genome sequencing of these six cases’ Listeria monocytogenes indicated that they likely had the same source of infection (wgMLST within 0-10 alleles). A suspect exposure was first identified based on several case histories, and food/environmental samples were collected from this location; although it was not clear what common exposure the initial cases may have had at this location. No Listeria was detected from these samples. Grocery store overlaps were also investigated. Eventually, shared exposure to Frugals, located at 10727 Pacific Ave S, Tacoma, WA 98444, was identified.No other Frugals locations (in Washington or Montana) were suspected.

Previous inspections at this location noted issues centered around hand washing; The Tacoma-Pierce County inspector noted an employee, wearing gloves, who handled raw beef and, after throwing those gloves away and putting on new ones, handled hamburger buns. The employee should have washed their hands in between the glove replacement. Of note, swabbing from areas such as the machine tubing, where Listeria can grow, is not required in routine inspections, so no such swabbing was done at this earlier inspection. The report also cited three minor infractions, those deemed not high-risk but still against regulations: A box of onions was on the floor but should have been placed on a shelf at least six inches off the ground; Gloves were found to be stored in the restroom area, which is not permitted; and a food processor meant for home use was on the premises, no longer in use.

An outbreak-response Environmental Health visit was conducted at Frugals on August 8, 2023 by the Tacoma-Pierce County Health Department. The inspector reviewed the manual for the Taylor 5454 machine while on site. The manual specified that the inlet and tubing must be cleaned with a scrub brush. No scrub brushes were available at time of inspection, and the cleaning process outlined by an employee did not include the cleaning of tubing. The employee explained that the tubing is only replaced when broken. The inspector also noticed a small crack in the holding bin of machine 1, that day. The facility was told it may not serve shakes or use either shake machine until approved by the Tacoma-Pierce County Health Department. The Washington state food code “requires restaurants use a pasteurized ingredient and follow the evaluated cleaning requirements set by the manufacturer unless they have a unique operating plan approved by the health department.” 

Samples of each finished milkshake flavor, a sample of unopened milkshake mix, and swabs from various parts of the interiors of the two milkshake machines were collected. Listeria monocytogenes was found in all milkshake flavors sold at Frugals at the time of the inspection. Swabs from the milkshake machines also detected Listeria monocytogenes.Whole genome sequencing of the organism found in the milkshakes and on the machines identified the outbreak strain. Preliminary results from unopened milkshake mix tested negative for Listeria.

Potentially contaminated milkshakes were sold prior to August 8, 2023, when the restaurant voluntarily discontinued use of the milkshake machines. Frugals also temporarily stopped using its machines at its other locations in Washington and Montana “out of an abundance of caution,” to have all of them sanitized and tested by a third party. In a statement issued on September 6, Frugals announced that “milkshake machines from its six locations outside of Tacoma have all been independently lab-tested. As expected, all samples have come back negative for the presence of Listeria.” Frugals also cited missteps in its cleaning regimen, while adding that, despite not being routinely checked by the local health department, “the machines in Tacoma have always undergone a rigorous weekly cleaning.”  The company said it discovered that “the manufacturer’s recommended cleaning tool was not being used for a portion of the process at the Tacoma location, and this may have allowed for a buildup of the Listeria bacteria.” [1]