As the United States’ holiday season rapidly approaches, there are growing concerns over a Salmonella outbreak linked to the centerpiece of many Thanksgiving meals. Last year, we shared a post that highlighted some common health-related Thanksgiving concerns amongst an array of festive puns. This year, we want to focus on one of those aforementioned concerns: food safety. This post will discuss the investigation of the ongoing Salmonella outbreak, and the overall burden of domestic foodborne illnesses.

Status of the Current Outbreak

This salmonella outbreak has incurred 164 cases and has spanned over 35 states. Cases began to be reported in November of last year, with 74 of them coming in since the last report update in late July. These cases have resulted in a sizeable number of hospitalizations and one death. Multiple agencies have held an ongoing investigation into this outbreak, and while they have uncovered a good deal of information, there are a number of crucial questions still unanswered.

Investigation into a foodborne outbreak requires collaboration between an array of professionals at local, state, and federal levels. The majority of outbreaks start at a local level and garner more attention as the outbreak progresses. When outbreak investigations require assistance at the federal level three main agencies play roles in the response. The Food Safety and Inspection Service (FSIS), a branch of the USDA, the Food and Drug Administration, and the CDC all have unique roles that advance the investigation of foodborne pathogens while simultaneously taking steps to protect the health and well-being of the US population.

After seeing an initial number of salmonella cases late last year, health officials reached out to patients to conduct interviews and reviewed patterns in their food consumption. The officials running this investigation found that over half of the interviewed individuals reported having contact with raw turkey prior to contracting salmonella, leading them to explore turkey meat as the potential source of contamination. The investigation identified the outbreak strain in a variety of forms including raw turkey products, certain pet food, and in live birds themselves. Specimens were identified in the homes of patients, in a number processing plants, and in over 20 slaughter houses. Investigators conducted whole genome sequencing of contaminated products found in these locations, and the results support the finding that they are all of the same strain.

Despite this growing pool of evidence, health officials are still searching for singular source of the outbreak. Since the same strain of salmonella has been seen across multiple states and within an assortment of products, there are concerns that the source of contamination lies at a higher level in the turkey production process. The investigation is still ongoing, and until the source of the outbreak comes to light, there are large questions for how to best quell its spread.

The Impact of Foodborne Disease Outbreaks

Salmonella is just one of many foodborne diseases that puts holiday meals at risk. The CDC estimates that in the United States alone foodborne pathogens account for almost 48 million illnesses each year. Of these cases, over 125,000 require hospitalization and around 3,000 prove fatal. It can be incredibly difficult to show that these cases are the result of large scale outbreaks, and even when linked, source attribution can perplex epidemiological experts. Part of this issue stems from challenges with surveillance, with a large number of foodborne illnesses often going unreported.

These estimates demonstrate a clear impact on the health of the domestic population, and additional modeling efforts have tried to quantify the burden foodborne illness plays in domestic public health. The USDA analyzed the 15 pathogens that account for the majority of foodborne disease, and estimated that their summative cost was over $15 billion per year. Salmonella, the focal point of this piece, accounted for the largest chunk of the costs with an estimated economic impact of $3.6 billion per year. Economic models are an imperfect measurement for the real burden of disease, but even still, the large numbers associated with foodborne illness help illustrate how detrimental their occurrence can be.

These estimates are paired with large amounts of uncertainty. Economic impact assessments try to combine the total costs generated from factors like required medical attention, amount of time incapacitated by disease, and amount of business lost from contaminated products. These models are based off of reported cases, a fraction that represents only a small portion of the total number of cases.

Unknown cases and challenges in disease surveillance are universal issues in most facets of foodborne illness reporting and response. The CDC uses a number of systems to monitor for new outbreaks and to identify their risk factors or trends when they appear. Searching for the culprit responsible in a foodborne outbreak relies on confirmed cases to provide valuable data points. This new information can influence the direction of future public health response efforts and identify issues in the food production process that, when addressed, make products safer for the population as a whole.

On a global scale, the impact of foodborne illness is magnified to a degree larger than domestic numbers. In their most recent report, the WHO suggested that 31 foodborne hazards account for approximately 600 million illnesses each year. Of these cases, experts suggest that over 400,000 result in death. The ability to control foodborne disease outbreaks resides in a structured public health system, and it is evident that these diseases provide a large challenge for the future of global public health outbreak control.

Getting back to the turkey

In time, the current turkey-linked salmonella outbreak will end and will represent only a small fraction of domestic foodborne illness that occur this year. Effective outbreak control and continued investigation should elucidate the contamination source and prevent future cases of disease. After the source discovery, there will be a number of potential actions that those leading the investigation can take to ensure the safety of consumers across the country.

Currently, the USDA is facing pressure from consumer protection organizations to reveal additional information before next week’s holiday. The USDA has pushed back against this, citing that FSIS has yet to identify the source of the contaminated meat, arguing that a definitive answer is needed before taking further action.  Given the current timeline of this investigation, it is unlikely that there will be an answer before turkey’s big day next week. In their most recent investigation notice, the CDC has not advised consumers to avoid this Thanksgiving centerpiece, but rather, they are urging consumers to practice safe food preparation practices to reduce the chances of illness. With this in mind, the Outbreak Observatory wanted to re-share resources from last year’s post, to ensure that those celebrating with this popular poultry product have a safe and happy holiday.

Photo: Several Salmonella sp. bacteria (red) invading an immune cell (yellow). Courtesy of National Institute of Allergy and Infectious Diseases (NIAID) via CDC.

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.