Frozen berries might seem like an unlikely source of illness, but they have been linked to outbreaks of hepatitis A around the world, including in New Zealand.
Unlike many bacteria, hepatitis A virus survives freezing, meaning it can remain infectious for years on contaminated foods such as frozen berries. Heating can destroy the virus, but berries are commonly eaten fresh and uncooked. Contamination can occur at any stage of production, from growing and harvesting through to processing and handling, particularly where hygiene practices or water quality are inadequate.
Hepatitis A is not endemic in New Zealand, and most cases are associated with overseas travel to countries where the virus is more common. Vaccination is recommended for travellers to these regions and provides effective protection.
When someone is diagnosed with hepatitis A but has not travelled overseas, it raises the possibility of a local source of infection, including contaminated food. This is where genomic sequencing becomes a powerful public health tool.
By comparing the genetic sequences of viruses from different cases, PHF Science scientists can identify cases that are likely to be linked through a common source, such as a contaminated food product. Working alongside epidemiologists and public health teams, PHF Science experts combine sequencing results with exposure histories to help identify potential outbreaks early and guide public health investigations and responses.
New Zealand's 2022–2023 hepatitis A outbreak linked to imported frozen berries highlighted the importance of this work. The outbreak affected dozens of people and led to strengthened import requirements for frozen berries.
It's just one example of how PHF Science scientists contribute to New Zealand's food safety system by using genomic surveillance to support the detection and investigation of foodborne virus outbreaks.