Safeguarding Against False Test Results

The larger the area we source our food from, the more we encounter the threat posed by a microscopic enemy: Foodborne pathogens. Good safety practices demand stringent, broad-spectrum testing to identify potentially dangerous microbes, but are the current testing products and procedures doing an adequate job? According to a recent report from the American Proficiency Institute, an independent agency that measures the accuracy of laboratories, there is significant room for improvement. New technology and new iterations of existing technologies hope to fill that need.

The food supply is becoming more and more global. Much of the produce, meat, and seafood found in U.S. markets and restaurants come from other countries. In fact, more than half of the food consumed on the planet is eaten in a different geography than it is grown or produced in. This opens our food supply to not only pathogens found locally, but also to microorganisms from all over the world.

Problematic Pathogens

Two of the most problematic pathogens are Salmonella and Campylobacter. As few as one to 10 Salmonella cells can cause disease, while 1,000 Campylobacter cells in contaminated poultry, raw milk, or produce can make a consumer ill. Of course, cooking does eliminate these pathogens, but food may still be handled between the time it is cooked and when it is served, opening up the possibility of bacteria being introduced by food handlers or servers.

Salmonella is the leading cause of foodborne illness according to FoodNet, the Centers for Disease Control and Prevention system for tracking foodborne infections. The number of Salmonella infections has remained relatively steady since 1996; however, there has been a shift in the strains sickening consumers. Wendy Lauer, senior product manager of Bio-Rad Laboratories, a San Francisco-based lab equipment provider, states, “Organisms continue to change and adapt. We have seen an increase in antibiotic-resistant Salmonella, for example. As a provider of solutions to the food industry, we have scientists working hard to keep up with these changes.” Infections from the most common strain have decreased, while illnesses caused by rising new strains, especially antibiotic-resistant strains, have increased. Infections from Campylobacter, the pathogen responsible for the third largest number of foodborne infections, are up 14 percent from the period between 2006 and 2008.

Mistakes in the Lab?

In May 2013, a report issued by the American Proficiency Institute and presented at the 113th General Meeting of the American Society for Microbiology revealed that over the past 14 years, the laboratories it has tested have shown significant gaps in accuracy when testing for disease-causing bacteria including Salmonella and Campylobacter. On average, participating labs had a false negative result rate (meaning bacteria was present when the test showed no pathogens) of 4.9 for Salmonella and 9.1 for Campylobacter. False positives (indicating bacteria was present when it was not) occurred at a rate of 3.9 percent for Salmonella.

Christopher Snabes, food technical specialist with the American Proficiency Institute, explains that it is unrealistic to expect that all labs would be error-free. No testing method and no testing facility is foolproof, and the largest variable is the human factor. According to Snabes, a number of errors can produce false negatives or false positives. For one thing, the lab technician can test for the wrong bacteria, or confuse samples and their target bacteria. A sample infected with Campylobacter will appear clean if only tested for Salmonella. Sometimes a recently emerged strain of bacteria has not yet been included in a lab’s pathogen database, or a technician makes a mathematical or transcription error. In proficiency testing, these mistakes result in a black mark, but in real life, the consequences can be deadly if a disease-causing pathogen finds its way into the food supply and sickens consumers.