You may have heard of the large outbreak of hepatitis A virus (HAV) last summer that affected over 1,000 Europeans in multiple countries and was tied to eating frozen berries. This prompted huge international investigations, and the European Food Safety Authority recently published a report on what was learned through traceback investigations on the berries. Here are some of the highlights:
The outbreak: In May 2013, officials in Germany began reporting cases of HAV in people who had recently traveled to Italy. Around that time, officials in Italy had been noticing the rise in cases in their country and declared an outbreak. In the end, 331 cases were confirmed by laboratory testing, out of 1444 cases reported in people from Denmark, Finland, France, Germany, Ireland, Norway, the Netherlands, Poland, Sweden, and the UK. 90% of the reported cases were in Italy.
The investigations: Several of the countries investigated the outbreaks within their borders. For example, Italy performed a retrospective case-control study and found that eating berries was the highest risk factor for getting the disease, with cases almost 5 times more likely to have eaten them than the controls. A study in Ireland found that 91% of the cases had eaten one or more products containing frozen berries.
The different nations shared their data, and 43 lots of berries were implicated as a likely source of the virus. Blackberries from Bulgaria and redcurrants from Poland were the most common ingredients in these 43 lots. Laboratory testing of the berries identified 16 lots that were contaminated with the virus, though it is difficult to detect small amounts of virus in large quantities of product, meaning the contamination could have been more widespread.
Facilities that processed and froze the berries were suggested as a common link, but no single point of contamination was found that could explain the whole outbreak. This led the investigators to make two theories:
- That there was actually a common source of the virus, such as from the farms sharing irrigation water, equipment, or employee time, but that these overlaps made it too complex to be able to pinpoint a source.
- That multiple people in the different facilities became sick at roughly the same time, and each contaminated some of the produce.
Doing the tracebacks was not a simple matter. For example, the lots most connected with illness were not all processed at the same facility, nor were they made of berries from the same supplier or farms in the same country. As another example, some of the Bulgarian blackberries had been picked by locals in public areas and forests, meaning there was not a specific farm they could be traced to.
The impact: While recalls did pull the products off of store shelves and European consumers have been asked to cook frozen berries before eating them, there is a chance some of the frozen berries could still be out there. The outbreak spurred public health officials in Europe to advocate more strongly for Good Hygiene Practices, Good Manufacturing Practices, and Good Agricultural Practices in the countries that make and freeze berries.