Food virus testing advice and result interpretation

Testing food for viruses is very different from routine bacteriological testing. ViroSafety provides independent specialist advice on food virus testing strategy, ISO 15216 and interpretation of laboratory results. ViroSafety is not a testing laboratory and does not perform food virus analyses.

When should food be tested for viruses?

Testing may be considered during outbreak investigations, incident investigations, verification exercises, supplier or process investigations, research, or where a specific risk question needs to be addressed. The value of testing depends heavily on the question being asked, the sampling plan, the food matrix, the timing of sampling and how the result will be interpreted.

Norovirus and hepatitis A testing

ISO 15216 provides standardised molecular methods for detection and quantification of norovirus and hepatitis A virus in specified food matrices using real-time RT-PCR. These methods detect viral RNA. A positive molecular result does not, by itself, prove that infectious virus is present.

What does a positive PCR result mean?

Interpretation should consider the analytical method, controls, result format, sample type, sampling location, epidemiological evidence and reason for testing. Detection of viral RNA may provide important evidence of contamination, but molecular detection and demonstration of infectivity are not the same thing.

What does a negative result mean?

A negative result applies to the sample tested. It should not automatically be interpreted as proof that an entire batch, production environment or supply chain is free from virus. Viral contamination can be heterogeneous, and sampling strategy is therefore central to interpretation.

Independent interpretation of food virus results

ViroSafety can help food businesses and other organisations understand what laboratory findings mean in practice, assess whether the testing approach addresses the question being asked, and place results in the wider food safety and epidemiological context.

This can include advice on norovirus and hepatitis A results, ISO 15216, recovery and process controls, RT-PCR findings, sampling considerations and the limitations of molecular detection.

Learn more about foodborne viruses

See the ViroSafety guide to foodborne viruses, the specialist norovirus and hepatitis A pages, or the self-paced Foodborne Viruses course.