Initial test
A test known as polymerase chain reaction (PCR) is used to screen food for Shiga toxin genes (stx1 and stx2).
The result of the PCR test will indicate whether those toxin genes are present or absent in the sample. Where no genes are detected this is considered a negative result. Where the genes are detected, further tests are needed to determine whether STEC is present.
Negative PCR test result
No actions will normally be required. Food businesses should continue to apply their normal controls, sampling and testing regimes as laid down in the FBO's FSMS/HACCP plan.
Positive PCR test result
This is known as a presumptive positive result which indicates that the stx genes are present.
The ACMSF's risk assessment shows it is not possible to determine the public health risk based on the presence of stx genes alone i.e. the presumptive positive results. This is because the stx genes can be detected in the absence of viable E. coli cells or they may be present in other organisms or as free DNA.
In most circumstances, a presumptive positive result would trigger further confirmatory tests but would not require risk management action. However, the food business or enforcing authority may decide to take action at this stage, where the risk assessment suggests that interventions, such as removing the food from the market, are necessary to protect public health. This would be based on additional information such as evidence of a breakdown in food safety management or a link to a foodborne illness outbreak, which indicates that contamination may have occurred, and the affected food may be unsafe.