A case–control study identified frozen berries eaten in smoothies as a potential vehicle but no specific type of berry, brand or origin of berries has yet been identified.
A foodborne outbreak of hepatitis A in Denmark was notified to other countries on 1 March 2013 and subsequently Finland, Norway and Sweden also identified an increased number of hepatitis A patients without travel history.
Most cases reported having eaten frozen berries at the time of exposure, reported Gillesberg et al in Eurosurveillance.
Denmark registered a higher than usual number of notified patients with hepatitis A virus (HAV) infection who had no travel history two-six weeks before symptom onset or other known risk factors for HAV infection in February 2013.
As of 17 April 2013, a total of 35 cases, including 13 confirmed, and two secondary cases have been identified in Denmark.
21 were female and the median age was 22 years (range: 4–66 years). Date of symptom onset ranged from 1 October 2012 to 27 March 2013 and two families with two and three cases respectively, as well as a group of four friends exposed at the same time, were identified.
A case study to identify the source of the infection included 25 probable and confirmed cases and 50 controls.
The researchers found 18 had eaten frozen berries used in freshly prepared smoothies and 20 had eaten frozen strawberries.
Statistically significant associations were found univariably with frozen foods such as strawberries, raspberries, blueberries, other berries and dates, figs and sun-dried tomatoes eaten in a dish other than salad or a sandwich.
Other Nordic countries affected
Finland, Norway and Sweden also reported an increase in the number of patients with HAV infection who had no history of foreign travel.
Each country identified one or more cases with HAV genotype 1B that had identical sequences to the HAV of the Danish cases.
As of 17 April 2013, 36 cases, 15 that were confirmed, have been identified in Finland, Norway and Sweden.
The overall median age for cases and the median age for confirmed cases is 25 years (range: 3–78 years); 43 cases are female. In Norway and Sweden (but not Finland), more women are affected than men.
“Given the long shelf life of frozen products, the long incubation time of HAV of 28–30 days (range: 15–50 days) and the potential delay in notifications, more cases will probably still be notified in the four countries,” detailed the report.
“The four national public health institutes and food authorities are therefore collaborating closely in order to confirm the source of the outbreak and stop further transmission.”
Source: Eurosurveillance, Volume 18, Issue 17, 25 April 2013
“Ongoing multi-strain foodborne Hepatitis A outbreak with frozen berries as suspected vehicle: four nordic countries affected, October 2012 to April 2013”
Authors: Gillesberg Lassen S, Soborg B, Midgley SE, Steens A, Vold L, Stene-Johansen K, Rimhanen-Finne R, Kontio M, Löfdahl M, Sundqvist L, Edelstein M, Jensen T, Vestergaard HT, Fischer TK, Mølbak K, Ethelberg S