Survival of Foodborne Pathogens on Berries
Fresh and frozen berries are popular foods. When berries are picked for fresh consumption, they are usually packed directly without washing because they are highly perishable. Fresh berries also are commonly included in fresh-cut fruit mixtures sold as a ready-to-eat product. Berries may be washed before freezing, but they are not usually blanched or heat-treated unless they will be used in preserves or other processed products. There is typically no “kill step” that would eliminate pathogens on fresh or frozen berries.
Foodborne illness outbreaks have been associated with the consumption of fresh or frozen berries that were contaminated with pathogenic viruses, parasites, or bacteria. Contamination can occur before or during harvest or during final preparation (Palumbo et al. 2013). The majority of outbreaks have been caused by viruses or parasites, and many of the virus-associated outbreaks have been linked to frozen berries. Outbreaks caused by viruses and parasitic coccidia are likely underreported because these pathogens are much more difficult to isolate and to study in the laboratory. Bacteria can be cultured on laboratory media, but viruses and coccidia require a host cell, often in the form of tissue culture. Norovirus, a common intestinal pathogen, cannot be grown in cell culture with currently available methods. Norovirus can be studied indirectly by using surrogate viruses or with non-culture methods that use a technique known as reverse transcription PCR.