Multistate foodborne outbreaks cause a disproportionate number of deaths compared with single-state events, but enhanced steps by industry can help blunt the impact, the US Centers for Disease Control and Prevention (CDC) said today in a Vital Signs report.
The CDC's analysis of outbreaks from 2010 to 2014 found that multistate events are linked to 56% of all foodborne outbreak-related deaths even though they made up just 3% of all outbreaks. An outside expert, however, said that addressing multistate outbreaks is important, but there are pitfalls in comparing ones that cross state lines with more local events.
At a media briefing today, CDC director Tom Frieden, MD, MPH, said, "Americans should not have to worry about getting sick from the food they eat." He added that analyses of multistate outbreaks are yielding lessons about food safety problems on farms or with food distribution.
Three culprits key
In its report today the CDC said multistate outbreaks are more dangerous than single-state outbreaks, because they often involve Salmonella, Escherichia coli, and Listeria and can contaminated widely distributed food items—such as vegetables, beef, chicken, and fresh fruit—that can sicken people in several states.
Researchers compared the number of illnesses, hospitalizations, and deaths from outbreaks in two or more states with outbreaks that occurred in a single state. Their analysis included 120 multistate outbreaks over the 5-year study span. They found that the multistate events were linked to 11% of all foodborne outbreak cases and 34% of hospitalizations.
Frieden said it's puzzling why multistate outbreaks seem to be more deadly, but he said the pathogens involved in the outbreaks generally cause more serious illness. He added that the numbers don't tell the whole story, that for each case there are several unreported cases, and some of the outbreaks involve multidrug-resistant Salmonella strains.
Multistate outbreaks can be difficult to detect and investigate, and health officials have a hard time tracing contaminated food to its source, but new methods such as DNA sequencing are helping match isolates from patients to those from contaminated foods, Frieden said.
He noted that more sophisticated investigation techniques are helping health officials identify contaminated foods that haven't been linked to outbreaks before, such as Listeria-tainted caramel apples that last year sickened 35 people in 12 states, 7 of them fatally. Frieden added that consolidation in food production networks means that contaminated food items are more likely to be distributed to many different states.
Evolving food industry roles
Federal health officials said today that their agencies are taking more steps to improve food safety, driven by implementation of the 2011 Food Safety Modernization Act. Also, the US Department of Agriculture (USDA) has proposed new industry standards for ground chicken and ground turkey and early next year hopes to tighten Salmonella standards for beef and pork.
"Overall, the food supply is safe, but it could be safer," he said.
The CDC said the report sheds light on a larger safety role for food companies—for example, following best practices for growing, processing, and shipping, keeping detailed records to help trace foods from source to destination, using store loyalty cards to help identify contaminated foods during outbreaks, and notifying customers of food recalls.
Expert: Outbreak types difficult to compare
Craig Hedberg, PhD, a food safety expert in the University of Minnesota's School of Public Health, told CIDRAP News that multistate outbreaks are clearly very important, but he raised issues with how the CDC compared the two types of outbreaks.
Comparing multistate events to single-state ones is "a little bit like comparing apples and oranges," he said. For example, he noted that federal officials don't truly have a way to track norovirus, so outbreaks involving that contamination source appear to be isolated local events.
And for Salmonella, multistate outbreaks are a concern because of their size, but the rates of hospitalization and death are the same for events involving single or multiple states, Hedberg added. Salmonella is the leading cause of foodborne illness, and though rates haven't changed much at all over the past several years, improvements in some food segments have been seen. Contamination, though, is coming from different sources than previously recognized.
Factors that play a role in foodborne illnesses outbreaks—the agent, host, and environment—are changing all the time, Hedberg said, noting that the rising role of drug-resistant strains is one example. "We can't get too comfy with what we think we know," he said.
The report seems to overpromote the use of technology in outbreak response, Hedberg said, and it seems underplay the importance of epidemiologic interviews with informational trace-back done in a timely manner in outbreak settings. He added that what seems to be missing is a focused sense of how to better use surveillance.
Nov 3 CDC Vital Signs report
Nov 3 full MMWR report
Nov 3 CDC press release