Health Officials’ Latest Tool in Tool Box – Whole Genome Sequencing
In late October, the Food and Drug Administration (FDA), Centers for Disease Control and Prevention (CDC), along with state and local officials investigated an outbreak of E. coli infections linked to food served at a major fast-casual restaurant chain. Much of the underlying information documenting the outbreak has been derived from an advanced laboratory technique called “whole genome sequencing” (WGS). This is a fairly new instrument in the CDC toolbox. WGS reveals the complete DNA make-up of an organism, thereby enabling health officials to better understand variations both within and between potentially pathogenic species. Such information can then be compared with clinical isolates from sick patients, and, if they match, there may be a reliable link established between the illness and the pathogen. This new technique has the potential to define the scope of a foodborne illness outbreak more quickly and ideally will help to prevent additional cases. Traditionally, this analysis has been done via a process known as pulse-field gel electrophoresis (PFGE). But PFGE has a shortcoming in that it is unable to differentiate between related species of organisms, which can be critical when health officials are trying to delineate the specific source of the outbreak, and want to know whether to recall a product or not.
The FDA cites numerous examples of how it has used WGS: 1
To differentiate sources of contamination, even within the same outbreak;
To determine which ingredient in a multi-ingredient food harbored the pathogen associated with an illness outbreak;
To narrow the search for the source of a contaminated ingredient;
As a clue to the possible source of illnesses; and
To determine unexpected vectors for food contamination.
The use of techniques such as WGS reflects FDA’s shift toward a broader preventative-centric approach to food safety. This approach can be associated the Food Safety Modernization Act (FSMA), signed into law on January 4, 2011, which requires comprehensive, science-based preventive controls across the food supply.2 FSMA provides the FDA with new enforcement authorities designed to achieve higher rates of compliance with prevention-based and risk-based food safety standards, and to better respond to and contain problems when they do occur. Lastly, the law also gives the FDA important new tools to hold imported foods to the same standards as domestic foods and directs FDA to build an integrated national food safety system in partnership with state and local authorities.
WGS also has been employed in the context of recent illness outbreaks associated with products regulated by the Food Safety and Inspection Service (FSIS), which oversees the safety of meat and poultry. In some circumstances involving FSIS, the regulated industry has found itself on the receiving end of confusing scientific input, as regulatory recommendations based upon PFGE analysis were subsequently negated by WGS data.
A shift to WGS may allow health officials to more quickly and more precisely connect the dots during an outbreak, and use of this tool may also benefit the regulated community. The enhanced precision of WGS may provide the regulated community with a new ability to prevent being falsely labeled as the source of the outbreak. Under the prior testing regime, PFGE tests were often unable to differentiate between related species of organisms, and as a result, regulators were at times forced to cast an overly wide net to capture the source of an outbreak. The new WGS technique provides authorities with a more precise and accurate tool. But, as circumstances with FSIS suggest, companies may also encounter confusion over growing pains associated with the movement from one generation of technology to another. We will continue to monitor the development and use of new tools and techniques the FDA, FSIS, and other federal agencies are using to prevent and respond to food safety issues.
1 Food and Drug Administration, Examples of How FDA Has Used Whole Genome Sequencing of Foodborne Pathogens For Regulatory Purposes, (last visited Nov. 9, 2015).
2 FDA Food Safety and Modernization Act, Pub. L. No. 111-353, 124 Stat. 3885 (2001).