Salmonella outbreaks study finds adulterant declaration might help prevent illnesses due to certain chicken products

The not ready-to-eat breaded, stuffed chicken products that are the target of new USDA regulations to declare Salmonella as an adulterant have often been the source of Salmonella outbreaks.

The Background

According to a new study, from 1998–2022, 11 Salmonella outbreaks linked to these products were reported; 57 percent of samples per outbreak from patient homes and retail stores yielded Salmonella. Outbreaks continue to occur, although fewer patients reported cooking the product in a microwave after labeling changes.

The number of patients who became ill from these products is likely much higher than that indicated by outbreak reports, the authors said. Many persons regularly eat these products: in a U.S. population survey, 7.4 percent reported eating these products in the previous week.

The researchers’ findings include the fact that outbreaks have continued despite consumer-based interventions and that additional control measures for Salmonella contamination by manufacturers could reduce Salmonella-involved illnesses associated with these products.

The study, “Salmonella Outbreaks Associated with Not Ready-to-Eat Breaded, Stuffed Chicken Products—United States” was published by the Centers for Disease Control and Prevention in the “Morbidity and Mortality Weekly Report (MMWR).”

The Announced

The rulemaking to declare Salmonella an adulterant in breaded chicken products was announced on April 28, 2023, by USDA’s Food Safety and Inspection Service.

According to the study, not ready-to-eat (NRTE) breaded, stuffed chicken products (e.g., chicken stuffed with broccoli and cheese) typically have a crispy, browned exterior that can make them appear cooked.

These products have been repeatedly linked to U.S. salmonellosis outbreaks, despite changes to packaging initiated in 2006 to identify the products as raw and warn against preparing them in a microwave oven.

The FSIS proposal is to declare Salmonella an “adulterant* at levels of one colony forming unit per gram or higher in these products. Salmonella outbreaks associated with NRTE breaded, stuffed chicken products during 1998–2022 were summarized using reports in the CDC’s Foodborne Disease Outbreak Surveillance System (FDOSS), outbreak questionnaires, web postings, and data from the Minnesota Department of Health (MDH) and the U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS).

According to the report, 11 outbreaks were identified in FDOSS. Among cultured samples from products obtained from patients’ homes and from retail stores during 10 outbreaks, a median of 57 percent of cultures per outbreak yielded Salmonella.

The NRTE breaded, stuffed chicken products were produced in at least three establishments. In the seven most recent outbreaks, up to 75 percent of ill respondents reported cooking the product in a microwave and reported that they thought the product was sold fully cooked or did not know whether it needed to be throughly cooked.

It was sold raw or fully cooked. Outbreaks associated with these products have occurred despite changes to product labels that better inform consumers that the products are raw and provide instructions on safe preparation, indicating that consumer-targeted interventions are insufficient, the study found. Additional Salmonella controls at the manufacturer level to reduce contamination in ingredients might reduce illnesses attributable to NRTE breaded, stuffed chicken products, according to researchers.

State health officials submit reports of foodborne Salmonella outbreaks to FDOSS. A foodborne outbreak is defined as the occurrence of a similar illness associated with a common food exposure in two or more people. Salmonella outbreaks with mention of frozen, breaded, or stuffed chicken that occurred during 1998–2022 were identified in FDOSS; data for 2022 are incomplete. Search results were supplemented by information obtained from outbreak investigators, and a review of questionnaires administered to ill persons, web postings, product recall information, product sampling results, and data from MDH and FSIS.

To examine the cooking practices of ill persons in outbreaks, and whether they believed the product was sold fully cooked, data collected from patient interviews during Minnesota and multistate outbreak investigations were summarized. Responses from outbreaks occurring during 2008–2021, after labeling changes were initiated in 2006, were compared with those from earlier outbreaks. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.

A NRTE breaded, stuffed chicken product was the confirmed food vehicle in 11 Salmonella outbreaks that occurred during 1998–2022, comprising 187 cases of illness, 42 hospitalizations, and no deaths. The outbreaks were caused by Salmonella serotypes Enteritidis (seven outbreaks), Typhimurium (two), Heidelberg (one), and I 4,[5],12:i- (one). In 10 of the 11 outbreaks, the products were prepared in private homes. Outbreak illnesses were identified in 21 U.S. states; five of six single-state outbreaks occurred in Minnesota and illnesses occurred in Minnesota in every multistate outbreak. Among 139 patients for whom data from 10 outbreaks were available, 73 (53 percent) were male and 64 (42 percent) of 153 patients were aged 20–49 years.

NRTE breaded, stuffed chicken products were made with comminuted chicken in the three 2015 and 2021 outbreaks. The type of chicken used during earlier outbreaks was not documented. FSIS issued product recalls in six outbreaks and public health alerts in seven. Product samples were collected from patients’ homes in nine outbreaks and from retail stores in 10. A median of 57 percent (range = 0 percent to 100 percent) of samples per outbreak from patients’ homes and 57 percent (range = 11 percent to 93 percent) of samples per outbreak from retail stores yielded Salmonella upon culture. An isolate from at least one product matched the patients’ serotype or strain in every outbreak in which the product was sampled. The producing establishment was unknown for one outbreak; products in the other 10 outbreaks came from at least three producing establishments. Establishments “A” and “B” were implicated in five outbreaks each, and Establishment “C” was implicated in three outbreaks. Establishments A and C are still operating; they are two of the six U.S. establishments that make these products.

Among 47 patients in four outbreaks during 1998–2006 (before product labeling changes) who provided data on the appliance used to cook the product, a median of 85 percent per outbreak (range = 67 percent to 100 percent) reported cooking the product in a microwave; among 57 patients who provided these data from seven outbreaks during 2008–2021 (after labeling changes), a median of 20 percent per outbreak (range = 0 percent to 75 percent) reported cooking the product in a microwave. In four outbreaks that occurred during 1998–2006, among 37 patients who provided information about whether they thought the product was sold fully cooked, a median of 56 percent per outbreak (range = 33 percent to 100 percent) reported that they thought the product was sold fully cooked or did not know whether it was sold raw or fully cooked. In six outbreaks during 2008–2021, among 34 patients who provided this information, a median of 27 percent per outbreak (range = 0 percent to 75 percent) thought the product was sold fully cooked or did not know whether it was sold raw or fully cooked.

Eleven Salmonella outbreaks linked to NRTE breaded, stuffed chicken products (involving 187 patients) were reported in the United States during 1998–2022. Most of the products tested contained Salmonella. Products were produced by at least three establishments. Outbreaks have continued to occur despite changes made to product labels to better inform consumers and increase the percentages of persons who understand that the product is sold raw. Thus, stronger controls are needed to prevent illnesses associated with these products, researchers concluded.

NRTE breaded, stuffed chicken products can be made with various types of chicken, including comminuted, trimmings, or other parts. Certain chicken types are subject to FSIS performance standards, which are used to measure an establishment’s process control; the comminuted chicken used to make these products has the highest allowable percentage (13 of 52 [25 percent]) of Salmonella positives.

Canada enacted regulations for certain breaded chicken products after investigators identified 19 Salmonella outbreaks caused by NRTE breaded chicken products during 2015–2019. These products were not stuffed; most were chicken nuggets. The government introduced four control options in nonstuffed products to reduce Salmonella to below detectable amounts in these products In 2019, the incidence of illness caused by Salmonella Enteritidis, the serotype implicated in 89 percent of those outbreaks, was 33 percent lower than it was during 2015–2018 and 7 percent lower than during the baseline years 2010–2014.

Consumer-based interventions alone, such as improved product labels, have not been an effective solution, researchers found. In recent years, labels have recommended using a conventional oven rather than a microwave and using a food thermometer; however, a consumer research study found that even when consumers read the label, 12 percent did not realize the product was raw or partially cooked, and among consumers who owned a food thermometer, 52 percent reported that they typically did not use it while preparing these products.

Although labeling changes can help protect consumers, the questionnaire data show that some people who knew the product was raw and followed the cooking instructions still became ill. Moreover, label changes cannot address inequities in access to recommended cooking appliances.

Although implicated products were distributed nationally, MDH officials identified all multistate outbreaks and almost one-half of outbreaks had cases identified only in Minnesota, suggesting that some outbreaks occurred but were not identified in other states.

Illnesses even among people who reported using a conventional oven and knew the product was raw indicate that consumer-based interventions have been insufficient. The high rate of contamination of products in outbreaks and the lack of first recognition of multistate outbreaks by a state other than Minnesota suggest that the prevalence of illness because of these products is higher than that indicated by outbreaks. Moreover, only a small proportion of all Salmonella illnesses are identified as such.

Conclusion: 

Finally, the study said Illness could be reduced by enhanced Salmonella control at the manufacturers that produce these products. It said USDA’s proposal to declare Salmonella an adulterant in NRTE breaded and stuffed chicken products will bring additional focus to this public health problem and encourage producers to better control Salmonella in the ingredients used to produce these products.