Likely source is store-bought food tainted by Listeria — a bacterium that can move from the digestive tract to cause invasive infections of the bloodstream and central nervous system.
Further epidemiological investigation revealed that the strain of Listeria identified by lab tests for another senior citizen — one living in the Midwest — matched the Connecticut strain. The lab results were used to pinpoint the source — chicken salad that had been prepared in New York and sold in a Florida deli. YSPH staff interviewed the Connecticut man’s widow and determined he had vacationed in Florida shortly before becoming ill.
The outbreak ended with the manufacturer recalling hundreds of pounds of fresh and frozen meat and poultry products. No further deaths were traced to the company’s products, and the manufacturer had its facility thoroughly sanitized. Subsequent testing found no further traces of Listeria.
Fighting foodborne illnesses
The case of the contaminated chicken salad is only one of many instances of foodborne disease investigated by the school. Two programs at Yale — FoodNet and FoodCORE — work closely together and complement each other’s missions to monitor foodborne illnesses and identify and respond to outbreaks.
The Emerging Infections Program (EIP) at YSPH assists with both efforts in Connecticut. The Foodborne Diseases Active Surveillance Network, more commonly known as FoodNet, was established by the Centers for Disease Control and Prevention (CDC) in the mid 1990s; it conducts active population-based surveillance at 10 sites in the United States, including Connecticut. FoodNet tracks laboratory-confirmed infections, monitors illnesses caused by select pathogens commonly transmitted through food, and conducts surveys and epidemiological studies.
Meanwhile, the CDC’s Foodborne Diseases Centers for Outbreak Response Enhancement, known as FoodCORE and established in Connecticut last year, works at seven sites across the United States to help detect, investigate and respond to outbreaks. The two programs’ Connecticut sites collaborate with the Connecticut Department of Public Health (DPH) and the School of Public Health as well as with the CDC.
FoodNet provides a crucial line of defense by helping public health officials better understand the epidemiology of foodborne diseases caused by bacteria and parasites that can be transmitted when food is improperly handled, prepared or stored.
Despite stringent rules and enforcement efforts at various levels of government, the overall number of infections from tainted food remains fairly high; foodborne illnesses are a serious — and sometimes deadly — public health threat in Connecticut and beyond.
In 2012, there were 19,531 infections, 4,563 hospitalizations and 68 deaths associated with foodborne diseases and reported through the 10 FoodNet sites, according to the CDC’s Morbidity and Mortality Weekly Report. And these are just the cases in which those who became sick saw their doctors and the doctors ordered the appropriate lab tests to detect the various intestinal pathogens, says Sharon Hurd, M.P.H., the Connecticut FoodNet program coordinator at EIP. In Connecticut alone, 1,266 laboratory-confirmed cases of foodborne diseases were reported, including 289 hospitalizations and six deaths in the same year.
“Foodborne illness is an important public health threat in Connecticut and nationwide,” Hurd says. “It is important to continually monitor illness trends. Our programs help to provide more complete information on the burden of foodborne illness and the extent of outbreaks in our community.”
How it works
Connecticut’s FoodNet tracks every laboratory-confirmed case caused by seven bacterial pathogens — Salmonella; Shigella; Campylobacter; Escherichia coli (or E. coli) O157 and other non-O157 Shiga toxin-producing E. coli (STEC); Listeria monocytogenes; Yersinia enterocolitica; and Vibrio — and two parasites, Cryptosporidium and Cyclospora.
These cases are investigated and documented with the help of students from Yale College and the School of Public Health. The students review test results from every lab in the state for the pathogens tracked by the CDC, and their findings contribute to national statistics. Collectively, Connecticut and the nine other states with FoodNet sites monitor some 600 laboratories nationwide, covering about 15 percent of the U.S. population.
“FoodNet is responsible for over 100 variables that go to CDC and contribute to the completeness and accuracy of the data,” Hurd says. “We’re responsible for making sure that all cases of foodborne illness identified in the laboratories are reported and that nothing is missed. Without FoodNet, the CDC would just get basic surveillance information.” FoodNet active surveillance records information that captures demographics, onset of illness and symptoms, as well as the percentage of patients who were hospitalized and the percentage that died, she notes.
Public health officials know that there are far more cases of foodborne illnesses than those officially identified, so it is essential to learn as much as possible from each reported case, says Mary E. Patrick, M.P.H., the CDC’s FoodNet project coordinator. Data collection is essential to creating a big picture of foodborne disease over time for use by public health officials.
Cases of foodborne illness, meanwhile, are investigated and documented with the help of five YSPH students working with FoodCORE.As a matter of routine as well as when an outbreak occurs, the local health department, the state health department, and Yale epidemiologists and students work together to interview people with confirmed cases of foodborne illness.
Staff members gather data by calling the sick person directly, or in the case of a child or deceased patient, a close relative. Furthermore, they collect demographic, clinical, risk factors and other information, posing more than a dozen questions to help spot potential patterns; and critically, to prevent the illnesses from spreading. Local health officials can then use the information to take necessary steps.
Through the staff members’ interviews, for example, FoodCORE determines whether the person works in food preparation, direct patient care or a day care center. This information allows health officials to alert others who may have been exposed.
Sometimes when investigating an outbreak from a single event such as a party, the staff member discovers that another food was served that wasn’t on the menu, says Samantha Greissman, a Yale senior who is also in her first year at the Yale School of Public Health and a FoodNet/FoodCORE staff member. The information is then passed along to the outbreak coordinator at DPH, who updates the list.
The CDC, meanwhile, tracks metrics that are different from the data collected by municipal health departments, whose primary goal is to address the local public health threat. If the local health department interviews the patient and doesn’t ask all the questions that the CDC needs, FoodCORE staff attempts to fill the gaps, Greissman says.
“We just had two cases of E. coli where the local health department interviewed both patients and didn’t ask all the questions that we ask when we interview patients,” she says. “Basically, we were missing data that we needed to fill in.”
If patients do not answer their phones, FoodCORE has to find another way to collect the information. The search may require calling the hospital, doctor or lab to gather demographic data and such details as whether the patient traveled out of state or outside the United States.
Since FoodNet’s inception, the highly detailed data that the program collects have helped to form a more accurate picture of how people get sick from foodborne illness. This higher level of accuracy has led to increased regulation and oversight at the source as well as improved prevention information.
Data collection has also helped public health officials identify potential risks in order to educate the public. For example, children under 3 years old who ride in the baskets of grocery store shopping carts are at increased risk of contracting Salmonella or Campylobacter from packages containing chicken or raw meat; this finding was reported in a 2010 study published by Patrick, Hurd and others in the Journal of Food Protection (Children riding in the cart’s seat were less likely to be exposed). The report led to a public information campaign to encourage parents to use sanitizing wipes before placing children in shopping carts; to place children in the cart’s seat rather than the basket; and to place raw meat and poultry in plastic bags and away from children.
While no one wants to see people get sick during an outbreak, investigating the source under intense deadline pressure does make for exciting work, says Greissman, who plans to pursue a medical degree after her M.P.H., with the goal of becoming an infectious disease specialist.
“It’s in real time. It’s a little bit of a high-stress, busy situation,” she says. When there’s a Salmonella outbreak at a barbecue, for example, staff will be given a list of those in attendance. “You call one person and they say, ‘My cousin was sick.’ And they tell you the name and that person wasn’t on the list. This is another clue.” The students don’t take the lead in data analysis, but they know that the fruits of their research are crucial in identifying the source of the illness and ultimately, in protecting the public.
The addition of the Yale FoodCORE student team made a measurable difference in interviewing people with a foodborne illness, says Quyen Phan, an epidemiologist with the Connecticut health department. In the first year of FoodCORE, more than 80 percent of people with reported cases of Salmonella were interviewed, compared with about 50 percent in previous years.
“Rapid and thorough interviews enhance [the department of] public health’s ability to quickly detect and investigate potential outbreaks,” Phan says. “The faster we are able to identify and investigate outbreaks, the greater the chances of preventing further illness.”
While outbreaks from peanut butter, spinach or restaurant food grab the headlines, most foodborne illnesses are sporadic and not part of clusters, Hurd says. In many cases the exact source of the illness is never determined.
“It is difficult to find or pinpoint the cause of foodborne illness because the majority of foodborne illnesses occur as individual or sporadic cases and are not associated with an outbreak,” she says. “Outbreaks that were once contained locally are now seen on a national or even international scale.”
Preventing foodborne illness
There are a few simple steps people can take to prevent foodborne illness. Thoroughly cooking meat, fish, poultry and eggs kills the pathogens that cause foodborne illness. Food workers who wash their hands, wear gloves and don’t work when sick are less likely to contaminate food. Also, cooks should use separate cutting boards and knives for meat and produce.
“Food can be contaminated at the source or in the slaughterhouse,” Hurd says. “You can’t avoid everything, but what you can do on a personal level is watch what you do.” For example, she’s pleased to see that a growing number of restaurants will no longer serve undercooked or raw meat and runny eggs. If they do serve uncooked or undercooked food, they will often indicate on the menu that eating it puts people at risk of foodborne illness.
Since years of data collection show that children under age 5, pregnant women, people over 65 years old and those with compromised immune systems are at greatest risk, Hurd suggests that people belonging to these groups be especially careful.
Looking forward, farmers, the food and food service industries, regulatory agencies, consumers and public health officials will all have important roles in addressing and reducing the incidence of foodborne illness. But obstacles to slowing and stopping the contamination of food remain.
“There is still room for improvement,” Hurd says. “Regulatory controls, inspections and adherence to safety practices along the food chain can make a difference in contamination, but protecting the nation’s food supply requires resources. We need to strengthen and expand our national food safety efforts.”
Data collected by FoodNet, meanwhile, informs others who focus on the education and prevention side of public health, Hurd says. Analysis of their data also has increased public health officials’ understanding of foodborne illnesses. This heightened awareness is reflected in the amount of information now available on their websites.
Such diligent data collection also helps the CDC stay abreast of threats from emerging bacteria or bacteria in the process of mutation. “One of the activities of the Emerging Infections Program is to maintain the flexibility for emergency response to address new problems as they arise,” Hurd says. “Our FoodNet data, through both surveillance and studies, should continue to inform those programs that monitor and support food safety.”