According to Foodborne Diseases Active Surveillance Network’s report on foodborne illness in 2013, clinical laboratories used culture-independent diagnostic tests (CIDTs) to detect more than 20,000 infections. Now, the Centers for Disease Control and Prevention (CDC) has delved deeper into the data collected about these tests. microscope-ecoli-406CIDTs are attractive to clinicians because they can be faster than traditional methods of culturing and can detect bugs that would otherwise be difficult to find. But there are concerns that because these tests don’t distinguish among the strains and serotypes of pathogens, their increasing popularity could negatively impact the determination of antimicrobial resistance, detection of foodborne illness outbreaks, and monitoring of public health interventions. According to CDC’s new study, the proportion of clinical laboratories using a CIDT to detect Campylobacter increased from fewer than 3 percent of clinical laboratories in 2004 to 15 percent in 2014. And the use of antigen-based and DNA-based methods to detect Shiga toxin or the genes encoding the toxins increased from 11 percent in 2007 to 60 percent in 2014. CIDT methods are most often used in the detection of Campylobacter and Shiga toxin-producing Escherichia coli (STEC). Among the 5,614 positive CIDT reports FoodNet detected during 2012-2013, nearly half were not confirmed using culture. Only 22 percent of positive CIDT reports of Campylobacter were confirmed by culture, while another 44 percent were culture-negative, which may be explained by poor transport stability of the organism, but could also signify a high proportion of false-positives. For STEC, 92 percent of CIDT-positive tests were confirmed by culture. Another 5 percent were culture-negative and 4 percent were never cultured. In most FoodNet sites, states require that Shiga toxin-positive enrichment broths be sent to public health laboratories for confirmation, so the high proportion of culturing in these instances suggest labs are following the rules and best practices. CIDTs were used to detect a tiny proportion of Salmonella infections. While laboratories used only culture to detect 15,000 cases, culture-independent tests found only 308, and most of these were never cultured. “Overall, a concerning proportion of positive CIDT reports were not confirmed by culture, either because the specimen was not cultured or because a culture did not yield the pathogen,” read CDC’s report. Quantifying the impact of CIDTs on trends in disease incidence and burden is complicated because performance differs among tests, testing practices might be different between CIDTs and traditional methods depending on the patient or the clinician, and the available CIDTs for enteric pathogens don’t have subtyping capacity. “The increased reliance on CIDTs will create a burden for public health laboratories and will have a significant impact on clinical practice, outbreak detection, and the ability to monitor disease burden and trends,” CDC stated. Going forward, the authors of the report suggest the need for enhanced public health surveillance, for reflex culturing (culturing a specimen with a positive CIDT result), and for the development of new CIDTs that provide strain characterization.