Preliminary analysis of the case interviews on possible risk factors associated with the ongoing outbreak identified consumption of frozen mixed berries (redcurrant, blackberries, raspberries, blueberries) as potential vehicle of infection. The hypothesis that they could be implicated is strongly supported by the detection of HAV virus in a sample of frozen mixed berries.
The surveillance on these frozen mixed berries together with other food items potentially carrying the HAV (vegetables, seafood, and other food reported as potential risk factors by cases in the epidemiological investigation), has been intensified, to provide a clear picture of the distribution of the contaminated items and the risk of exposure through these.
The case-control study is currently ongoing; the results of this investigation will provide an opportunity to support the hypothesis of the likely source of infection and together with the molecular sequencing information will provide a picture of the genotypes in this outbreak to be compared to those circulating in the previous years in Italy and to those that are currently circulating in other countries.
Comparison of information from the tracing-back of positive frozen mixed berries with information obtained through the purchase history is ongoing.
Seven sequences of HAV genotype 1A isolated from cases in different countries (the Netherlands, Germany and Italy) and in different laboratories showed a 100% similarity. The genotype and the sequence of the virus isolated in the Italian outbreak is different from the currently ongoing outbreak with frozen berries as suspected vehicle described in northern European countries and in the United States.
Despite the great efforts made in the detection of positive food consignments and recall of those suspected or found positive, more cases are expected in the next weeks, due to the long incubation period of HAV (28–30 days; range: 15–50 days), the notification delay, and the long shelf life that frozen berries have.
The Italian public health authorities are collaborating closely in order to confirm the source of the outbreak and to stop further transmission.