Boise-Co-OpOn June 8-9, 2015 the Central District Health Department (CDHD) started receiving reports from Boise area health care providers about patients diagnosed with Salmonella. The common link identified in initial interviews with ill patients was food purchased after June 1 at the Boise Co-op deli section. Medical providers in the community were notified that a foodborne illness outbreak was possibly underway. They were encouraged to test patients who presented with symptoms consistent with a Salmonella infection. Public health agencies in Idaho and neighboring states were alerted about the potential outbreak. The Idaho Department of Health and Welfare (IDHW) assigned identification number OB 2015-068 to the investigation.

CDHD continued to receive reports of ill Boise Co-op deli customers over the next several weeks. CDHD established a call center to triage complaints to the agency’s epidemiology and environmental health units. Ill persons also had the option of completing an on-line questionnaire at the agency’s website. Health department staff gathered information about patient symptoms, foods consumed at the Boise Co-op and elsewhere, and other risk factors for infection with Salmonella. Laboratory testing of patient isolates determined that outbreak associated cases were infected with Salmonella Enteriditis, PFGE pattern JEGX01.0004.

CDHD Environmental Health staff conducted the first on-site visit to the Boise Co-op on June 9. Inspectors made suggestions for improving food handling practices and gathered food samples for laboratory testing. They were told that deli menu items could be made to order or customers could purchase “grab and go” deli prepared and packaged items. In addition to the store location, deli food was sold at a kiosk located in the Boise airport. Health department staff also learned that Co-op employees had been sick. On June 15 the Co-op voluntarily closed their store’s deli section and notified customers of the outbreak. CDHD staff recommended the deli be thoroughly cleaned and sanitized. Health department staff also instructed Co-op managers to develop a document outlining a detailed risk reduction plan looking at how food is received, stored, prepared and held in the deli section.

On June 17 CDHD Environmental Health staff met again with Co-op managers who said in addition to devising a risk control plan, they would be installing new sinks to further enhance food safety controls. On June 19 the Boise Co-op deli was allowed to reopen. Ill employees could not return to work until they had tested negative for Salmonella per Idaho laws.

Laboratory testing by the IDHW Bureau of Laboratories (BOL) revealed that several of the food samples collected by CDHD staff were positive for Salmonella Enteritidis. These included an onion sample and a sample of sliced tomatoes. Leftover cooked Boar’s Head brand turkey collected from a patient’s home also tested positive for Salmonella Enteritidis. A sample of raw turkey taken from the Co-op deli was positive for Salmonella Heidelberg.

Outbreak associated cases as individuals who had eaten a Boise Co-Op made deli item purchased at either the store or the airport kiosk on or after June 2, 2015. Other outbreak cases were linked epidemiologically to ill Co-op customers. Case patients were classified as “confirmed, “probable” or “suspect” using the following criteria.

Confirmed Case:

A person who was laboratory confirmed with Salmonella by culture and ate a deli item, or
A person who was laboratory confirmed with Salmonella by culture who was linked epidemiologically to a person who ate Boise Co-op deli food.

Probable Case:

A person who was laboratory confirmed with Salmonella by PCR and ate a deli item, or
A person who had a clinically compatible illness and ate a deli item, or
A person who was linked epidemiologically to a confirmed case but who did not eat a deli item

Suspect case:

A person who was linked epidemiologically to a probable case but who did not eat a deli item, or
A person with a clinically compatible illness without information required to classify as an outbreak related probable case

The first date of illness in a Boise Co-op customer was June 3. This person reported eating a sandwich with onion and tomato, items that would both test positive for Salmonella. On July 2, 2015 CDHD reported a total of 294 outbreak associated cases. This total included 262 Central District residents, 11 residents who lived in Idaho but outside of the Central District Health Department jurisdiction and 14 out of state residents. Among the 262 Central District residents there were 102 patients classified as “confirmed” cases, 132 patients classified as “probable” cases, and 28 patients classified as “suspect” cases. Of the 234 confirmed and probable cases identified as Central District Health Department cases, 170 (73%) sought medical care and 12 (5%) were hospitalized. The majority (186) consumed an item purchased at the store location versus the airport kiosk.

Public health investigators were unable to determine how Salmonella was introduced into Boise Co-op deli food. They concluded that the bacteria were likely spread through cross contamination and poor personal hygiene practices by employees.