There is no such thing as zero risk when it comes to food safety, according to researchers.

Consumers, industry and governments typically desire foods that are free of any risk but scientists said zero risk is unattainable in food production regardless of the severity of inactivation treatments or stringency of sampling programs.

Risk-based approaches such as Microbial Risk Assessment (MRA) are increasingly used to manage food safety hazards, evaluate risks and identify control strategies that reduce risks to an acceptable level.

Researchers Marcel Zwietering, Alberto Garre, Martin Wiedmann and Robert Buchanan presented the study, published in Current Opinion in Food Science, at IAFP Europe.

They defined residual risk as what remains even after a fully compliant food safety system has been implemented. Every product has a residual risk but severity varies because it depends on a variety of factors such as the perspective or consequences.

Traditional sampling limitations
Researchers said if decisions were based only on testing, it could falsely be concluded that if a hazard has not been detected, the associated risk must be zero.

“As an example, the fact that a given pathogen has never been detected in a product does not ensure that the implemented safety controls assure a hazard-free or zero risk product,” according to the researchers.

“Because sampling is limited, it is feasible that the microorganism entered the system at some point, but it was not yet detected or identified. Alternatively, it is also possible that the hazard has not yet entered the system, but that does not ensure it will never in the future. The absence of a positive is no proof of the absence of risk in the current, past or future.”

Researchers gave the example of the risk of Salmonella in chocolate bars assuming contamination of one Salmonella enterica cell per 10,000 of 25,000 bars of 25-grams, and that the company produces 100,000 bars a day. Testing is limited to five samples per day, each sampling unit is a whole bar, and probability of a false negative or false positive is zero.

“The probability of detecting Salmonella in each sampling unit equals 0.01 percent, and the probability of detecting it in the product in a given day is 0.05 percent. In other words, we expect a single positive every 5.5 years. On the basis of this result, it could seem reasonable to conclude that the risk of salmonellosis is insignificant.

“However, a single cell of Salmonella enterica has a probability of causing illness that has been estimated to be 1 case per 400. Therefore, if we consider that 10 bars of the 100,000 daily production contain a single Salmonella enterica cell, the expected number of yearly cases of salmonellosis is 9.125, a value that is certainly not insignificant. Although sampling will rarely show a positive, there is clearly a residual risk.”

Better tech and more production
Researchers said between large scale production lots with low levels of a pathogen and modern molecular epidemiology systems, there could be detection of an outbreak at levels below that which a manufacturer can verify by traditional testing. This was illustrated using the Salmonella and chocolate example.

Increases in the scale of manufacturing for dry products means production may take place over multiple days, weeks, or months without a break for complete hygienic cleaning of a facility. Globalization and the development of worldwide distribution increases the likelihood that a single, multi-day production lot could be sent to multiple countries, according to the study authors.

Improved surveillance systems such as those using whole genome sequencing can detect small outbreaks and potentially link cases to a product, even when they are consequences of residual risk rather than a non-compliant food safety system.

“This leads to the potential policy gaps when regulatory agencies or food distributors/retailers provide realistic and practical testing guidelines and specifications for foods that are substantially less stringent than the ability to detect a low-level outbreak after literally millions of servings have been consumed by the public. This hypothetical example shows how residual risks of microbial hazards is to be topic of substantial debate and legal challenges in the coming decades,” according to the study.