October 23, 2014

New Foodborne Illness Diagnostic Tests Make Outbreaks Harder to Detect

An article in Scientific American states that new diagnostic tests for common pathogenic bacteria such as E. coli, Salmonella, and Campylobacter may make it harder, if not impossible, for public health officials to detect multistate outbreaks. The new rapid nonculture tests do detect bacteria quickly, but further testing on the bacteria is impossible.

Traditional lab tests grow bacteria on a culture medium. An isolate of the bacterial colony is then sent to public health officials, who conduct pulsed field gel electrophoresis tests on the bacteria to determine its DNA fingerprint. That fingerprint is entered into the PulseNet system to see if it matches any other samples. If government officials find two or more illnesses from unrelated individuals with the same DNA fingerprint, they can declare an outbreak.

Declaring an outbreak means that an investigation is launched, traceback is conducted, and officials can find the source of the contamination, issue recalls, and fix the problem. Alicia Cronquist, an epidemiologist with the Colorado Department of Public Health and Environment said in the article there is a “clear shift in the types of tests being run in local labs … resulted in much less information being shared.” The new tests are less expensive and provide quicker results. They also diagnose more infections and find pathogens that cultured tests do not.

Tennessee state epidemiologist Timothy F. Jones stated in the article that “these rapid tests put us back where we were when we didn’t have the ability to do fingerprinting.” Since the USDA’s Microbiological Data Program is shutting down, and since rules from the Food Safety Modernization Act are not being published, this change to uncultured testing is troubling.

No one is trying to develop a test that will both provide rapid diagnostics and allow PFGE testing. The public health system is a critical safeguard to help contain foodborne illness outbreaks. Many more people could be sickened if non-culture testing continues.

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