The CDC is documenting more multistate foodborne disease outbreaks involving a wider range of food products and pathogens than ever before — 22 outbreaks in 2010 compared with 11 in 2006.
This year, more than 400 people in 28 states were affected from raw scraped ground tuna contaminated with Salmonella Bareilly and Salmonella Nchanga sold in sushi restaurants and grocery stores.
Two different strains of Salmonella in mangoes from both foreign and domestic distributors infected at least 127 people in 15 states. Listeria monocytogenes from imported ricotta salata cheese hospitalized 20 people and killed four in 14 states.
“US health authorities can no longer think in terms of securing a safe food supply just within the borders of the 50 states anymore,” William Schaffner, MD, professor of medicine in the department of infectious disease at Vanderbilt University in Nashville, Tenn., and an Infectious Disease News Editorial Board member, said in an interview.
At the same time, the US food supply has become more centralized. “A single large food supplier may distribute lots of food rapidly across large parts of the country, so when something is disrupted in that chain from farm to fork, it is now rapidly amplified throughout the entire system,” Ian Williams, PhD, MS, chief of the outbreak response and prevention branch in the CDC’s Division of Foodborne, Waterborne and Environmental Diseases, said in an interview with Infectious Disease News.
Kathleen Gensheimer, MD, MPH, said the CORE Network monitors potential foodborne disease clusters and is engaged early on during outbreaks.
Photo courtesy of Gensheimer K
Despite these growing complexities, experts in the infectious disease and public health communities are working hard to ensure that the US food supply is fit for consumption. “More frequent identification of outbreaks and potentially
contaminated products does not necessarily mean our food is less safe,” Schaffner said.
Instead, greater awareness of foodborne disease outbreaks is a sign that health officials and epidemiologists are succeeding in finding solutions to the challenges from our increasingly complex food supply system.
The CORE Network and FoodCORE
In January 2011, Congress passed the Food Safety and Modernization Act (FSMA), with the goal of creating modern preventive infection control measures for food and feed facilities, as well as mandatory science-based minimum standards for the safe harvesting of fruits and vegetables.
Under FSMA provisions, the FDA established the Coordinated Outbreak Response and Evaluation (CORE) Network in September 2011, a multidisciplinary cadre of 35 members that includes veterinarians, epidemiologists, policy analysts, environmental health specialists and consumer safety officers.
The CORE Network goes above and beyond the traditional outbreak response of simply identifying a food product that is causing illness and removing it from the market, according to Kathleen Gensheimer, MD, MPH, chief medical officer and director of the CORE Network, and an Infectious Disease News Editorial Board member.
“We want to monitor potential foodborne disease clusters and become engaged earlier on, apply the more typical response component to stop the outbreak and to pull the implicated food off the market. Then we take what’s been learned from these investigations and put it to good use, so we can put preventive practices, policy or educational outreach efforts into place,” Gensheimer said.
The FDA’s CORE Network does not work in a vacuum, she added. Collaboration with epidemiologists at the CDC, public health officials and agricultural officials at the state and local level, as well as laboratory partners, are essential to its success.
Besides the FDA’s CORE Network, the CDC has formed its own analogous unit in the Outbreak Response and Prevention Branch called the Outbreak Response Team, composed of 10 people who investigate 20 to 40 multistate foodborne disease outbreaks each week. This team then works with FDA’s CORE Network to perform the regulatory actions necessary to get affected products off the market. CDC also coordinates the Foodborne Disease Centers for Outbreak Response Enhancement (FoodCORE) program to enhance the ability of state and local health departments to respond to foodborne disease outbreaks.
“Part of what FoodCORE is trying to do is determine how to best perform outbreak response activities and then put these theories into practice. It’s the CDC’s laboratory for building model practices for outbreak response,” Williams said.
More efficient investigations
Recent upticks in foodborne disease outbreaks are a paradoxical effect of improvements in outbreak detection, according to Schaffner. The number of foodborne disease outbreaks investigated by CDC has increased from about 50 in 2006 to 180 in 2011-2012.
“We are identifying foodborne illnesses more quickly and more precisely, and we are better able to distinguish local contamination from products that are distributed commercially,” Schaffner said.
Besides increasing the volume of investigations, the FDA and CDC teams are conducting them more efficiently.
During its first year, FoodCORE labs decreased the average time it spent serotyping Salmonella isolates from 8 days to 4 days, and the epidemiology group decreased the time it took to attempt to identify a listeriosis case from 7 days to 1 day.
Another key component is PulseNET, a national network of laboratories that perform standardized molecular fingerprinting using pulsed-field gel electrophoresis (PFGE). PFGE enables investigators to distinguish strains of foodborne disease-causing bacteria, such as Escherichia coli, Salmonella, Shigella, Listeria and Campylobacter, at the DNA level.
“When a patient visits their doctor with an illness caused by Salmonella, for example, that isolate is then stored in a public health laboratory, and the organism’s DNA fingerprint is electronically transmitted to the central PulseNet database at the CDC,” Williams said.
PulseNet is searchable on-demand by partners at state health departments, local health departments and federal agencies, enabling them to compare strains and communicate in real-time to identify common sources of foodborne disease outbreaks.
“We’re constantly looking at PulseNet to see if we can find clusters of illness,” Williams said. “For example, if we expect to see two cases with a specific Salmonella fingerprint during a 60-day period and we now have 10 cases, we know that’s above background, and it’s time to start to investigating the cluster to see if the people who became ill share something in common.”
Both the CDC’s Outbreak Response Team and the FDA’s CORE Network monitor clusters of disease via PulseNet, and the two agencies meet weekly to exchange information.
If a pathogen is detected in a particular product that falls within the regulatory jurisdiction of FDA — a food, animal, cosmetic or dietary supplement shipped using interstate commerce — the agency communicates this information to the CDC. The CDC can then work with epidemiologists at the state and local levels to incorporate specific food product information into questionnaires used in the outbreak investigations.
This multidisciplinary effort gives teams a more complete picture of what to look for in outbreak investigations, according to Gwen Biggerstaff, MSPH, an epidemiologist in the CDC’s outbreak response and prevention branch in the Division of Foodborne, Waterborne and Environmental Diseases.
“If investigators are going into a restaurant and they know the epidemiology, they have a better idea of what might be causing people to get sick, so they can tailor their environmental health assessment to get the information that’s the most critical for the investigation,” Biggerstaff said.
Improved outbreak outcomes
The March outbreak of Salmonella infections involving raw scraped ground tuna is a prime example of how multidisciplinary interagency investigations can untangle complex foodborne disease outbreaks and successfully prevent additional illness.
Epidemiologists at FoodCORE’s seven centers in Connecticut, Ohio, New York, South Carolina, Tennessee, Utah and Wisconsin were among the first to provide critical information that helped accelerate this investigation, according to Biggerstaff.
Laboratory tests on bacteria isolated from ill people at FoodCORE centers identified an unusual Salmonella serotype— Salmonella Bareilly. Then investigators conducted specific interviews with people about what they had eaten leading up to their illness.
“Once we knew it was sushi, we looked for places that we could trace this product back to, and we were able to identify four restaurant clusters where illnesses were occurring,” Williams said. “We then passed this information back to the FDA.”
“The CDC and state and local epidemiology and regulatory programs were able to determine that the illness was linked to consumption of either a seafood product or a sushi roll,” Gensheimer said. “But as you interview people, they can tell you they ate sushi, but they generally do not know the specific ingredients consumed that comprised their sushi roll. Hence, we not only had a growing multi-state outbreak, but a complex multi-ingredient product that was undoubtedly implicated with illness. Investigators had to look for common ingredients utilized by sushi chefs. Answers to questions regarding type of rice, seaweed, seasonings, sauces, and of course, the specific type of fish used to prepare the sushi were sought. What became clear was that many different variations became evident in how sushi was prepared, depending on the chef,” she said.
So the FDA honed in on the four identified restaurant clusters and set about verifying and tracing back each component ingredient in the sushi rolls, obtaining product invoices and shipping orders to verify ingredients utilized. They also looked into determining which products were used at what times to detect any correlations between specific sushi components, when a case patient visited the restaurant and when illness onset occurred.
“This was a complex investigation that took 3 full weeks to complete after activation of the FDA Emergency Operations Center and with 39 people working full time at the FDA, but ultimately we were able to trace the outbreak back to a fishery in India,” Gensheimer said.
When FDA investigators went to that fishery, they were able to document unsanitary practices, which ultimately led the Indian government to close the facility.
Concurrently, a smaller cluster of Salmonella Nchanga was identified with cases also reporting a history of sushi consumption which were linked back to the Indian fishery.
“Because we investigated this warehouse facility, we were able to keep 56,000 lb of frozen ground scraped tuna from being distributed further,” Gensheimer said. “These corrective actions ensured that the product was not distributed to commerce, and I have no doubt that we prevented hundreds of other infections from occurring.”
The most recent large-scale outbreak investigated by these CDC and FDA teams led to the first-ever suspension of a manufacturer’s facility registration in late November, which prohibits the facility from distributing food, according to the FDA.
Since September, an outbreak of Salmonella Bredeney in peanut butter has resulted in more than 40 people with Salmonella infection in 20 states. The FDA found Salmonella in 28 environmental samples during its inspection of the plant in September and October 2012, in addition to 14 different product samples.
“The outbreak investigation by FoodCORE and the CORE Network provided vital information to inform the regulatory action. The fact that peanut butter made by the company has been linked to an outbreak of Salmonella Bredeney that has sickened 41 people in 20 states, coupled with Sunland’s history of violations led FDA to make the decision to suspend the company’s registration,” Gensheimer said.
The FDA will reinstate the manufacturer’s registration only when the agency determines the company has implemented procedures to produce safe products. Therefore, the investigation remains underway.
Robust post-outbreak response
CORE Network and CDC Outbreak Response Team investigators’ work does not finish when an outbreak ends.
“Each outbreak gives us an opportunity to learn about our food safety system. There is a cycle of response that we can go back and study to inform future policy recommendations,” Biggerstaff said.
This involves determining what gaps in the food safety system contributed to the outbreak, and then trying to fill in those gaps to keep similar outbreaks from happening again.
The CORE Network has dedicated post-response teams that look at all aspects of an outbreak — from ingredient sourcing to production and distribution. They then determine best practices to share with growers, food producers, processors, distributors and consumers.
For example, in the September 2011
L. monocytogenes outbreak involving whole fresh cantaloupes from Jensen Farms in Colorado, FDA’s post-response team performed a root cause analysis and environmental assessment to identify factors that may have contributed to contamination.
“We don’t know which specific factors lead to contamination — maybe it was a mix of all of them together,” Gensheimer said. “But we were able to take this information back to melon producers so they could put measures in place to minimize the chance of another outbreak.
“No food processor, producer grower wants to be the subject of a foodborne illness outbreak investigation,” she added.
Flexibility in approach
There is no one-size-fits-all approach to detecting foodborne disease outbreaks. Public health departments in each state and large city are structured differently from one another, with each having their own way of doing things, adding up to much diversity within different state and city models.
“What works in Wisconsin may work for some other states, and what works in New York City may be applicable to other places, but with systems like FoodCORE and the CORE Network in place, we can identify model practices and then take them and implement them elsewhere,” Williams said.
“We all have a common goal, whether it’s FDA, CDC or state health departments. We are all trying to achieve better, faster investigations to shorten the time it takes to figure out what’s making people sick and to keep other people from getting ill,” Biggerstaff said.
It is also important to remember that success in investigating multistate foodborne disease outbreaks depends on clinicians being able to diagnose and report their findings appropriately. Although a clinician may only see one or two cases, it may be part of a much larger outbreak. “If the information is not communicated and reported up, then ultimately we won’t be able to identify the outbreak,” Williams said.
“Foodborne disease outbreaks are not going to disappear,” Gensheimer said. “Microbes will always find ways to outsmart us all, and we need to continue to find ways to deal proactively with these ongoing threats.” — by Nicole Blazek
CDC. CDC FoodCORE Team. www.cdc.gov/foodcore/team.html; Page last updated: July 5, 2012; accessed Nov. 28, 2012. FDA. Coordinated Outbreak Response and Evaluation (CORE) Network.
www.fda.gov/Food/FoodSafety/CORENetwork/default.htm; Page Last Updated: Nov. 17, 2012; accessed Nov. 28, 2012.
For more information:
Gwen Biggerstaff, MSPH, can be reached at Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC, 1600 Clifton Road - MS A38, Atlanta, GA 30333.
Kathleen F. Gensheimer, MD, MPH, can be reached at Office of the Deputy Commissioner for Foods, U.S. Food and Drug Administration, 4300 River Road, HFS-015, College Park, MD 20740; email: Kathleen.Gensheimer@fda.hhs.gov
William Schaffner, MD, can be reached at 1500 21st Ave. South, Suite 2600; Nashville, TN 37212; email: William.email@example.com
Ian Williams, PhD, MS, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC, 1600 Clifton Road - MS A38, Atlanta, GA 30333.
Disclosure: Biggerstaff, Gensheimer, Schaffner and Williams report no relevant financial disclosures.