By George Miller
If nothing else, the recent Salmonella Saintpaul outbreak from contaminated jalapeño and serrano peppers demonstrates that food trace-back in the global supply chain requires a combination of resources, coordination, and speed. It also requires a strategic balance of proactive and reactive tactics.
But another requirement is persistence of effort, during both outbreak and non-outbreak times, especially in encouraging the public to seek medical help when people get sick.
“Education of the public is perhaps the most important tool in fighting food-borne illness at the global level,” says Rob Donofrio, M.S., Ph.D. candidate, director for microbiology at NSF International (Ann Arbor, MI), an independent, not-for-profit organization that writes standards for food, water, and consumer goods protection.
He adds that sick people are the most timely data points in a trace-back investigation. By August 14, the victim count had reached 1,423. Yet even when victims go to a hospital, days will already have passed since they ingested the affected food, and memories of food eaten and ingredients used will be fading.
During a trace-back investigation, technology tools come into play when stool samples from sufferers become available for use by investigators in identifying the contamination culprit.
“The detection techniques are there,” says Donofrio. “But the time required to get a DNA fingerprint still includes the time it takes to grow the organism.”
Spreading the word
Once investigators find what they believe may be the beginnings of an outbreak, they need to inform other members of the health-care community to spread the word and identify similar cases. In the U.S. investigators activate PulseNet–a national network of public health and food regulatory agency labs coordinated by the Centers for Disease Control and Prevention (CDC). PulseNet encompasses state and local health departments as well as federal agencies. So its labs, expertise, and database capabilities are available to trace-back investigators at all levels: national, state, and local.
PulseNet investigators perform standardized molecular subtyping (DNA fingerprinting) of food-borne disease-causing bacteria using pulsed-field gel electrophoresis (PFGE). PFGE helps investigators distinguish strains of organisms such as Escherichia coli O157:H7, Salmonella, Shigella, Listeria, and Campylobacter.
The effort can get expensive, says Donofrio. So the states that are able to make such investments–$70,000 to $100,000 for a riboprinter; $30,000 to $50,000 for electrophoresis gear, plus people to run the equipment and analyze results–will have a decided advantage over those unable to do so, who must ship samples to federal facilities and await results before resuming an investigation.
Minnesota is one of the lucky states having such equipment, according to Kirk Smith, food-borne disease supervisor at the Minnesota Department of Health. The department has staff members “who have the expertise to interpret lab results, and who just happen to be good at detective work,” he says.
Smith and his team tracked the state’s Salmonella Saintpaul outbreak from its first appearance in Minnesota, sharing information with CDC and FDA, and eventually confirming that they were working on the same outbreak.
The Minnesota team traced the outbreak to a Texas distribution facility and eventually to the Mexican farm, with federal investigators apprised and involved via FoodNet, CDC’s Foodborne Diseases Active Surveillance Network.
“We have more people focused on food-borne illnesses than other states,” says Smith, in part because of its relationship with CDC. “As a member of FoodNet, we get money from CDC to use on our own resources, as well as using its resources.”
Minnesota employs a centralized trace-back system that starts when the clinical lab sends Smith’s office DNA-fingerprinting results, usually complete within two or three days of receiving stool samples. “Then we start interviews, and we continue conducting them on a real-time basis, as soon as we can reach victims.”
Smith places great importance on the interviews. “If you don’t collect the information right away, it’s that much harder to get because people forget,” he explains.
In the Minnesota Salmonella Saintpaul trace-back operation, Smith’s lab received 10 isolates between June 23 and 27. “That’s a lot,” he notes. “We usually don’t get 10 in a year.”
Smith’s team began interviewing victims. A victim from the second interview, conducted on July 29, identified the restaurant later found to be the cause of Minnesota’s outbreak. “It’s a Mexican restaurant in the Twin Cities, a table-service restaurant,” Smith says. (The name of the restaurant was not released at press time.) He started a full-blown investigation on July 30.
“We asked people what they ate, which menu items, which ingredients they remember, and whether any ingredients were added or removed,” he says. “Then we find and interview people who ate at the same restaurant around the same time, both those who got sick and those who didn’t.”
Figure 2. An automated immunoassay instrument is one tool FDA chemists use to detect cell surface antigens of Salmonella on food products. Photo courtesy of FDA.
Investigators then visited the restaurant, checking the meals and appetizers served on the day in question. They determined the ingredients used in what the victims ate, and then got the restaurant’s vendor invoices for its purchase of those ingredients. It turns out that the restaurant used the contaminated jalapeño peppers primarily as a garnish.
A hot trail
Following the source of an invoice, Minnesota investigators visited a Texas distribution facility–Agricola Zaragoza Inc. of McAllen, TX, a big produce warehouse used by several distributors–where they found the “smoking pepper.” Agricola issued a recall on July 21 for peppers distributed since the end of June.
From Texas, the pepper was traced to a packing facility in Nuevo Leon, Mexico, and then to a farm in Tamaulipas, Mexico. A second contaminated product was found at the packing facility and traced to another farm in Tamaulipas.
Further investigation at the first farm led researchers to believe that contaminated irrigation water, produced via runoff after the farmer used animal manure as fertilizer, or contaminated water used to rinse or clean peppers, was most likely the source.
“There are more outbreaks that we don’t solve than we do,” says Smith. “Most clusters involve three to ten reported illnesses. But when they get this big, we tend to solve them.”