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In the first half of 2013, Europe dealt with three simultaneous outbreaks from the hepatitis A virus. Knowing that at least two of those outbreaks were connected to frozen berries, Europe’s Centre for Disease Prevention and Control set out to describe what could be learned from those outbreaks in an article published in Eurosurveillance.
Those three outbreaks resulted in 400 confirmed cases between 15 European Union countries and Switzerland.
The first report of hepatitis A illness occurred in Denmark on March 1. The virus then cropped up in Finland, Norway and Sweden, ultimately infecting 106 people. Epidemiological investigations traced those cases to frozen strawberries grown in Egypt and Morocco, though health investigators testing the strawberries could not find hard evidence of hepatitis A contamination.
The second outbreak was reported in Norway on April 17 and was soon reported in another 13 countries. That outbreak affected 107 travelers who had all recently visited Egypt, and the outbreak strain of the virus had the same subgenotype as the first outbreak associated with strawberries.
An epidemiological investigation into the second outbreak suggested the likely source was strawberries or another fruit distributed to hotels in Egypt.
The third outbreak was reported in Germany on May 8, after nine Germans were infected with hepatitis A after traveling to Italy. This third outbreak is believed to have infected about 200 Italian residents, as well as one Dutch traveler and five Polish travelers.
Curiously, another 21 Irish residents with no travel history to Italy were infected by the same strain of the virus.
Separate investigations in Italy and Ireland both implicated imported frozen mixed berries as the source, with most of those berries coming from Eastern Europe.
But despite the fact that all three outbreaks were associated with imported fruits, the researchers say they aren’t related.
First, the Italy/Ireland outbreak was caused by an entirely different subgenotype than the other two outbreaks, meaning that the viruses weren’t related. But even with the two outbreaks associated with imported strawberries, those viruses differed genetically to the point that investigators knew they weren’t the same virus, although the two pathogens likely originated from the same geographical region.
“Having three multi-country outbreaks declared within three months is an unexpected situation,” the report says.
But a few factors likely contributed to creating the perfect storm in which large numbers of Europeans suffered from hepatitis A infections.
First, Europe had seen declining numbers of hepatitis A infections in the past decade, meaning that fewer people in the population had developed antibodies to repel the virus. Couple that with the fact that hepatitis A was not on the vaccination schedule for citizens of many of the countries affected, and the result was a highly susceptible population.
Most of the European travelers to Egypt were not advised to get hepatitis A vaccinations when staying in all-inclusive resorts, while at the same time an increasing number of Europeans were traveling to Egypt.
Further, the investigators believe contamination of the berries occurred early in the food production chain.
Investigators suspect that irrigation water contaminated with sewage water likely tainted the strawberries in the two outbreaks connected to Egypt. But the contamination might have also been caused by infected workers in the field or the processing facility, or by contaminated water sprayed on the berries sometime before distribution.
The investigators also suspect that the first outbreak in the Nordic countries might have triggered heightened surveillance for hepatitis A across Europe, thus enabling health officials in those countries to be alert enough to detect the other outbreaks, which might have otherwise gone undetected by authorities.
“The outbreaks described have shown that frozen berries are efficient vehicles of [hepatitis A virus] infection; to this extent, the risk posed by berries should be studied further,” the report says.
Those studies could include analyzing the opportunities for berry contamination and the likelihood of exposure to hepatitis A from berries in Europe.
The early detection of the separate outbreaks was made possible by the Epidemic Intelligence Information System for Food- and Water-borne Diseases (EPIS-FWD) within the ECDC. The agency’s rapid sequencing of DNA/RNA allowed for the identification and linking of dispersed cases.
The European Commission and ECDC “should play a role in ensuring that adequate capacity to isolate and sequence [hepatitis A virus] in food and human samples is available at the EU level, through promoting common protocols and sharing expertise,” the report says.
For multi-country outbreaks, coordination of traceback and monitoring resources is essential. Importers should also work closely with their producers to ensure they’re meeting sufficient food safety practices and ensure that cooperative traceback can take place in the event of an outbreak.
Finally, the outbreak involving travel to Egypt highlights the need for travelers to receive vaccinations when traveling to areas with endemic diseases.
The report warns that more hepatitis A outbreaks can be expected in Europe until the lessons from these three recent outbreaks can be taken into account.
“The 2013 experience demonstrates the absolute necessity for extensive collaboration between countries and between the public health and food sectors to identify as quickly as possible the vehicle of infection and, ideally, to control the outbreak in an timely fashion.”
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