Culture-independent diagnostic tests offer better food-borne infection incidence estimates, but without isolates, laboratories are unable to subtype pathogens, determine antimicrobial susceptibility, and detect outbreaks.
Despite many efforts made in the fight against food-borne illnesses, outbreaks continue to spring up throughout the United States, underscoring the fact that further prevention measures are desperately needed to reduce the incidence of these infections.
A report recently issued by the Centers for Disease Control and Prevention (CDC) shared preliminary data pertaining to changes in incidence of food-borne infections since 2006, highlighted which pathogens seem to be on the rise as well as which efforts are currently working. Also emphasized in the report was the growing use of culture-independent diagnostic tests (CIDTs) in clinical laboratories and the pros and cons of these tests.
Using data collected by the Foodborne Diseases Active Surveillance Network (FoodNet) which monitors cases of laboratory-diagnosed infections caused by 9 food-borne pathogens across 10 US sites, CDC researchers found that in 2017 alone, 24,484 infections, 5,677 hospitalizations, and 122 deaths were reported.
Incidence of all of the following pathogens was noted to have increased compared with 2014 to 2016 data: Campylobacter, Listeria, non-)157 Shiga toxin-producing Escherichia coli (STEC), Yersinia, Vibrio, and Cyclospora. However, it was noted that increases in incidence could potentially be attributed to an increase in the use of CIDTs. Older methods, such as routine stool tests, were only able to identify a limited number of food-borne pathogens. CIDTs help reveal more accurate incidence estimates, according to the report.
Although the incidence of infections with Salmonella serotypes Typhimurium and Heidelberg decreased in 2017 compared with 2006 to 2008, the incidence of other Salmonella serotypes such as Javiana, Infantis, and Thompson, actually increased by about 50% each. Due to these increases, overall incidence of Salmonella has not substantially declined since 2014 to 2016.
Authors of the report attribute new regulatory requirements created to improve testing for Salmonella in poultry products as a potential contributor to the decrease in some of the serotypes; vaccination in poultry flocks may have also helped, although there is not enough data available to be certain. The report also highlighted a decrease in STEC O157 infections in 2017 compared with 2006 to 2008.
“The declines in 2 Salmonella serotypes and STEC O157 infections provide supportive evidence that targeted control measures are effective,” the authors write. “The marked increases in infections caused by some Salmonella serotypes provide an opportunity to investigate food and nonfood sources of infection and to design specific interventions.”
Although increased use of CIDTs allows for more accurate incidence estimates of food-borne infections, when reflex culture is not performed, laboratories are not able to subtype pathogens, determine antimicrobial susceptibility, and detect outbreaks. In addition, CIDTs are also known to vary when it comes to sensitivity and specificity. The Association of Public Health Laboratories recommends that clinical laboratories culture specimens that are CIDT-positive; however, 25% of bacterial infections in 2017 were not cultured.
“More control measures are needed and might be achieved with the continued implementation of the FDA Food Safety Modernization Act, new or revised meat and poultry performance standards, and enhanced training and guidance for industry and inspection personnel,” the authors write. “In particular, measures targeting specific Salmonella serotypes, including vaccination of broiler poultry flocks, might result in a marked decrease in human illness, as has been seen in the United Kingdom.”