Understanding confirmation test failures for detecting pathogenic E. coli

Summary

The United States of America is Australia's second largest beef export market with shipments in 2011 reaching 167,820 tonnes at an estimated value of $774 million. Manufacturing beef or beef trim comprises a substantial proportion of beef exports and it is an export requirement that product is tested for E. coli O157 prior to being sent to the USA. As of June 2012 this requirement extended to an additional six serotypes of pathogenic STEC (pSTEC). One aspect of the pSTEC testing process that has come under additional scrutiny in recent times is the ratio of potential positives (i.e screening test positive) to presumptive and/or confirmed positives. Samples that test positive during a screening test but subsequently fail to yield a confirmed isolate are called negative and able to be exported.
There is some concern that failure to convert potential positives into confirmed positives may result in contaminated product leaving Australia for export markets and this could result in a positive point of entry (POE) detection in the USA. Several POE detections have already occurred and the current Australian red meat industry process of testing and confirming pSTEC has been questioned by the US Food Safety and Inspection Service who operate the POE testing program. A recent baseline survey on the prevalence of pSTEC in manufacturing beef concluded that the conversion rate of potential positives to confirmed positive is also low and similar concerns about Australian beef testing positive at Port of entry for pSTEC are likely if data relating to why samples aren't confirmed as positive are not generated. This study aims to investigate whether or not pathogenic E. coli are present in samples that test positive by screening methods and in turn will determine possible reasons for the failure to isolate pathogenic E. coli through routine testing.