Recent food safety recalls involving nuts highlight the challenges facing food processors in the 21st Century. In April 2011, a cluster of 14 cases of food-borne illness with E. coli O157 was detected in Canada. Two of these persons developed hemolytic uremic syndrome (HUS), a serious complication that can lead to kidney failure; one person died from the illness. Genetic analysis of the strains recovered from these patients indicated a common source of the infection, triggering a public health investigation.
Epidemiologists were able to statistically link the illnesses to the consumption of shelled walnuts distributed by a Canadian firm, prompting a product recall. These nuts were traced back through the distribution chain to several California processors. The link to California was strengthened by the discovery of a US illness in Wisconsin involving the same strain of E. coli. This individual also consumed walnuts that came through the same distribution chain from the same processors as the products implicated in Canada.
Although E. coli O157:H7 is most commonly associated with foods such as beef, fruit juices and leafy greens, this is not the first such incident involving low moisture foods. Raw cookie dough distributed by a major food processor caused 65 U.S. cases of E. coli O157:H7 illness in 2009. An investigation by the firm implicated the raw bulk flour as the contaminated ingredient and prompted a switch to a heat-treated bagged product. In March, eight cases of O157:H7 infection scattered across four US states were traced to contaminated in-shell hazelnuts. Another Canadian recall of imported US walnuts occurred in September after a consumer became ill with E. coli O157:H7.
Would microbiological testing of these products have prevented these illnesses? Massive sampling of the cookie dough ingredients eventually detected a single positive hit on raw flour. Samples of the in-shell hazelnuts and the walnuts recalled in September also tested positive for E. coli O157:H7. However, product sampling and analysis did not prove useful in the April walnut recall. In that incident, numerous samples of walnuts recovered from the processors, the Canadian distributor and the victims tested negative for E. coli O157. Environmental samples from the handler & distributor facilities also tested negative. Collectively, the evidence from these recalls points to low, sporadic levels of contamination. Detecting microbes in these situations is like finding a “needle in a haystack”!
A few decades ago, these recalls would not have happened. The small number of illnesses that occurred would have flown under public health radar. Modern genetic techniques, the Internet and classic epidemiology are the keys to cracking these cases. A collection of DNA testing methods with tongue-twisting names like pulse-field gel electrophoresis (PFGE) and multiple-locus variable-number tandem-repeats analysis (MLVA) are used to pinpoint the identities of bacterial strains from these outbreaks. This information is shared online by public health authorities in database program called PulseNet.
When a cluster of matching strains is detected, epidemiologists go to work. They interview the patients with this illness and determine what foods they have eaten; analysis of the resulting information is used to determine the common source of contamination. In the April recall, the statistical correlation was high enough to assure regulatory authorities that walnuts were the cause, despite negative sample test results.
These incidents demonstrate the increasing importance of food safety programs in today’s world. Technology has given us the ability to detect sporadic, isolated cases of food-borne illness; the level of contamination involved in these events is very low. Finished product testing is simply not enough-rigorous preventative programs that combine Good Agricultural Practices (GAPs), Good Manufacturing Practices (GMPs) and Hazard Analysis Critical Control Points (HACCP) are essential to ensure food safety. Intervention to reduce microbial risks is the only solution for food processors in today’s world: DFA is able and ready to help you meet that challenge and face the future!
