Hundreds of foodborne outbreaks may go undetected in US each year
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Key takeaways:
- More than 16,000 small foodborne outbreaks may have gone unreported between 1998 and 2019.
- The number of unreported outbreaks has decreased as use of whole-genome sequencing in surveillance has increased.
Researchers estimated that hundreds of small foodborne disease outbreaks may go undetected in the United States each year, based on a statistical analysis of data from the last 2-plus decades.
Laura Ford, PhD, an epidemiologist in the CDC’s Division of Foodborne, Waterborne, and Environmental Diseases, and colleagues found that foodborne disease outbreak data fits a power law distribution, statistical distribution in which one variable is proportional to the power of another variable — in this case showing that large outbreaks are rare, but small outbreaks are more common and, historically, have gone underreported.
Over time, however, as whole-genome sequencing (WGS) and PCR testing have come in to use at most U.S. public health laboratories, the number of undetected or underreported outbreaks has decreased, the researchers found.
CDC data show that as many as 800 foodborne outbreaks are reported annually in the U.S., causing roughly 14,000 illness and 800 hospitalizations. Outbreaks range from locally contaminated meals among family and friends to multistate outbreaks linked to widely distributed contaminated foods.
“Power law distribution parameters should be stable over time, but changes in the slope or minimum threshold or deviations from the estimated power law might indicate perturbations of concern,” Ford and colleagues wrote. “Understanding the different power law parameters that underlie outbreak size and frequency can be useful for exploring how detection of foodborne outbreaks differs by pathogen or food vehicle. In addition, those parameter changes can reflect public health interventions.”
The researchers studied data from the CDC’s Foodborne Disease Outbreak Surveillance System collected from 1998 to 2019, which included a total of 10,026 outbreaks, including those with two or fewer illnesses similar to others.
According to the study, a power law distribution fit outbreak data for both the 1998 to 2017 period, when there were 8,993 reported outbreaks, and the 2018 to 2019 period, when there were 1,033 reported outbreaks.
The researchers determined that 788 fewer than expected small outbreaks and one fewer than expected large outbreak were reported annually each year from 1998 to 2017, and 365 fewer outbreaks were reported during 2018 to 2019. The researchers credit some part of the improvement to widespread use of WGS in outbreak surveillance efforts.
Ford and colleagues said power law distribution analyses may have an application beyond foodborne outbreaks, and it has already been applied to COVID-19, measles and gonorrhea. Its use, they wrote, may help to predict outbreaks and better plan response needs for both routine and surge scenarios.
“We used power law distribution on foodborne disease outbreak data to quantify underdetection and how foodborne disease reporting has improved,” Ford and colleagues wrote. “The improvement in underdetection during 2018-2019 could in part be explained by improved detection or investigation from the implementation of WGS. The power law distribution can be used to assess the impact of past and future public health interventions and as a tool for resource planning.”
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