As of 6 August 2013, the Danish, Finnish, Norwegian and Swedish public health institutes reported 106 cases associated with the hepatitis A virus (HAV) infection outbreak affecting their countries since 1 October 2012. Of these, 64 were confirmed and 42 were probable.
Since the joint ECDC/EFSA rapid outbreak assessment on 15 April 2013 , the European case definition has been revised. The current case definition defines probable cases as residents of Denmark, Finland, Norway and Sweden, with onset of symptoms from 1 October 2012, no travel history outside of Western Europe two to six weeks before onset of symptoms and no known risk factors for HAV infection. A confirmed case is defined as a probable case infected with HAV sub-genotype IB and a sequence identical to one of the two closely related sequences identified in this outbreak .
Denmark reported 68 cases (38 confirmed), Finland 14 (7 confirmed), Norway seven (six confirmed) and Sweden 17 (13 confirmed). The median age of the cases is 23 years (ranging from 2 to 76) and 61% (n=65) are female.
Epidemiological investigations found cases more likely to have consumed frozen berries and strawberries than controls; purchase history investigations in Denmark pointed at frozen strawberries imported from North Africa and distributed in the four Nordic countries as the most likely vehicle of infection. Initially the four countries issued recommendations for boiling frozen berries before consumption; then, on 30 May 2013, the distributor in Denmark, Norway and Sweden voluntarily recalled the implicated product from the market [2-4].
The distribution of reported cases by the time of their symptoms’ onset and reporting country (figure 1) shows a steep decrease in the number of cases reported in the last months. Since the implicated vehicle of infection has long storage life and could be kept in household freezers for several months, it is possible that recent and new cases may be due to delayed and unaware consumption of the implicated food item.
ECDC continues to monitor this event together with the affected countries. The recommendations given in the rapid risk assessment of the 15 April 2013 remains unchanged . Three other food-borne HAV-related outbreaks are simultaneously under investigation in Italy and Ireland, among European travellers returning from Egypt and in the USA. At present, there is no evidence of common links between these outbreaks.
Figure 1: distribution of cases by month of onset and reporting country, hepatitis A outbreak in four Nordic countries, Oct 2012 - Jul 2013 (n=106)