Future of Produce Testing in Question

Salmonella in sprouts. Listeria in cantaloupe. Over the past year, highly publicized outbreaks make produce seem more and more threatening. But is that really the case, or is the U.S. making headway in the fight against foodborne illnesses? Well, there’s good news and bad news.

Bad news first. According to FoodNet, the CDC’s report card tracking food safety trends, Salmonella infections have increased by 3% over 2009, resulting in nearly three times the number of infections established as a national health objective target in 2010.

On the flip side, infections caused by six other key pathogens dropped significantly in 2010, including:

• Shigella (57% decrease);
• E. coli O157 (44% decrease); and
• Listeria (38% decrease).

An important key to controlling outbreaks and continuing this positive trend is identifying a pathogen quickly. One obstacle to early detection is the difference between the number of microorganisms it takes to make a person ill and the number that must be present in a sample to produce a positive assay result. To find an offending pathogen, produce samples must be “enriched”—treated so that the bacteria count is amplified. Enrichment broths, liquids that encourage the proliferation of a specific type of bacteria, are used to prepare samples for pathogen testing.

A more versatile enrichment broth, one that promotes rapid proliferation of multiple serotypes of various bacteria, can streamline the testing process. In July 2010, the Center for Food Safety at the University of Georgia in Griffin reported successfully testing an improved, universal enrichment broth used for Listeria and Salmonella. In addition, this broth contains a buffering agent that promotes pathogen growth by neutralizing bacterial-toxic acid.

Another challenge in outbreak control is time, which has been addressed by a new generation of laboratory testing platforms. Where once it took several days to evaluate a sample for STEC or Salmonella, the Atlas System, developed by Roka Bioscience of Warren, N.J., can produce results in less than a day. “This platform uses molecular technologies to deliver approximately 300 results in eight hours and about 500 results in 12 hours, all with a single operator,” said A.J. McCardell, Roka’s senior vice president of commercial operations. “In comparative studies, for every 250 samples run, Atlas saved 7.5 hours of direct labor.”

In addition, the Atlas System is fully automated. One operator can load sample tubes continuously, rather than waiting for a full batch, and all assay steps are completed by the single machine. Minimal touchpoints and color-coded, pre-printed labels mean a smaller margin of error. McCardell also pointed out its small size. “If there is a four-foot space along a wall in the lab, the Atlas system will fit.”

Gumshoe Science

Testing samples identifies the pathogen, but point of origin must be traced using phone calls and questionnaires—time-consuming, labor-intensive, and, therefore, expensive methods.

Each state health department is responsible for monitoring food safety and outbreaks within its own borders. In a multi-state outbreak of 200 cases, each state may see only a handful of illnesses. The number may not be compelling enough for a state to commit sufficient funds for the detective work.

To ease the burden, in 2009, the CDC funded a pilot project in three states to develop new and better methods to detect, investigate, respond to, and control multi-state outbreaks of foodborne illnesses, particularly Salmonella, STEC, and Listeria. This program, called FoodCORE [Foodborne Diseases Centers for Outbreak Response Enhancement], was successful enough to be expanded to seven states.