Batch testing for noroviruses in frozen raspberries

Area of Science:

• Food Safety
• Microbiology
• Public Health

Background:

• Raspberries are frequently linked to norovirus (NoV) outbreaks and product recalls.
• Contamination can occur in both raw materials and intermediate food products.
• Assessing viral contamination in frozen berries is crucial for food safety.

Purpose of the Study:

• To investigate the presence and levels of norovirus (GI and GII) in frozen raspberries.
• To evaluate the sanitary quality of frozen raspberries used for puree and frozen fruit mix production.
• To assess the effectiveness of sequencing for confirming RT-qPCR results.

Main Methods:

• Collected 130 frozen raspberry samples from 26 batches across four processing companies.
• Conducted enumeration of Escherichia coli and coliforms.
• Utilized real-time reverse transcription PCR (RT-qPCR) for norovirus detection (GI/GII) and sequencing for confirmation.

Main Results:

• Six of 70 samples from puree production batches tested positive for norovirus GI, with levels above the limit of quantification (4.3 log genomic copies/20g).
• Two batches were classified as having insufficient sanitary quality due to NoV presence.
• One batch of IQF raspberries tested weakly positive for NoV GI, below the limit of quantification; sequencing was successful for GI but often failed for GII.

Conclusions:

• Certain batches of frozen raspberries intended for puree production pose a sanitary quality concern due to significant norovirus contamination.
• The public health risk remains uncertain as RT-qPCR cannot distinguish between infectious and non-infectious virus particles.
• Sequencing confirmation protocols require optimization, particularly for GII norovirus detection.