Why Faster Foodborne Illness Tests Could Hamper Outbreak Tracking

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The CDC has released a report on the rates of foodborne illness from 2012-2015.

Although the overall rate of food poisoning cases has not varied much from year to year, the report notes an increasing trend in diagnostic testing that could affect the agency’s ability to identify and track foodborne outbreaks.

The growing problem is from the rise of culture-independent diagnostic tests (CIDT).

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CDC Report Looks at CIDT: Quick Facts

  • Foodborne illnesses are normally diagnosed by isolating and culturing (growing) bacteria samples to confirm the presence of something like salmonella
  • Culturing is accurate but time-consuming and has to be repeated for each possible bacteria
  • CIDT is a form of testing that can check samples for multiple types of bacteria and get results within hours, without the need for cultures
  • This speed allows foodborne illnesses to be diagnosed that might otherwise have been missed
  • Although it allows for individuals to be diagnosed faster, not all CIDT findings get confirmed with culturing
  • This is a problem because CIDT cannot distinguish between different strains or subtypes of bacteria and does not produce genetic isolates

In other words, CIDT allows for faster individual diagnoses but makes it harder to recognize and track outbreaks. This is because PulseNet, the system that the CDC uses to monitor and identify foodborne illness outbreaks, relies on a bacteria strain’s DNA fingerprint and other details.

The CDC report notes that in 2015, the FoodNet tracking system (which covers ~15% of the U.S population) reported 20,107 culture-confirmed infections but also saw 3,112 CIDT that didn’t get culture confirmation—roughly double the number from 2012.

What the Rise of CIDT Could Mean

CIDT is undeniable effective and meets an important diagnostic need. However, the CIDT findings are not compatible with PusleNet and positive results aren’t being cultured in every instance. This could lead to a situation where a foodborne outbreak is occurring but the CDC isn’t able to effectively recognize or track it since the necessary data simply isn’t available. To be clear, there is no current indication that things have reached this point, but it is a real possibility that the CDC is keeping in mind.

What Is Being Done About This?

There are current efforts underway to explore different methods PulseNet could work without the need for bacterial isolates from cultures. Some examples include next generation sequencing, a form of rapid genome sequencing, and metagenomics—a way of identifying genetic code from a patient’s sample.

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In the meantime, the CDC is working with other public health officials and laboratories to promote the testing and culturing of any CDIT-positive findings. Ways of making the storage and culturing process easier are also being investigated.

All of these measures are still in the early stage but they represent the continued evolution of food safety and outbreak tracking. PulseNet is currently 20 years old and the CDC fully intends to see the system remain agile and effective well into the future.


Sources:
Huang, J., et. al., “Infection with Pathogens Transmitted Commonly Through Food and the Effect of Increasing Use of Culture-Independent Diagnostic Tests on Surveillance — Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2012–2015,” Morbidity and Mortality Weekly Report, 2016; http://www.cdc.gov/mmwr/volumes/65/wr/mm6514a2.htm?s_cid=mm6514a2_x.
“The Future of PulseNet,” CDC web site, last updated February 16, 2016; http://www.cdc.gov/pulsenet/next-generation.html, last accessed April 15, 2016.