Between January and May 2013 a hepatitis A (HA) increase was detected in Italy, signalling an outbreak. A retrospective matched case–control study tried to identify the source of infection.
Epidemiological data showed an increase compared to the same period of the previous three years.
Control measures included recall of the confirmed frozen mixed berry batches and a trace-back investigation was started.
Since HAV genotyping and sequencing is not performed on a routine basis in Italy the researchers said they could not compare the outbreak genotype with previously identified Italian genotypes.
The European Food Safety Authority (EFSA) said recently that contaminated product could still be circulating as part of a wider Hepatitis A outbreak that has sickened at least 1,444, although the virus genotypes are different from the Italian outbreak.
Sequencing the virion protein (VP)1-2a region from 24 cases yielded a common sequence, said the report.
The same sequence was amplified from frozen mixed berries eaten by some cases as well as from isolates from Dutch and German patients, who had visited some of the affected Italian provinces during the outbreak.
The highest increase in numbers of patients affected was observed in northern Italy, in the regions of Emilia-Romagna, Friuli–Venezia-Giulia, Lombardy, Piedmont, Trento and Bolzano, and Veneto. Apulia (south Italy) also showed an increase in the number of cases in 2013.
In May 2013, some European Union Member States (Germany, Netherlands, Poland) reported cases linked to a ski holiday in northern Italy.
After this notification, a retrospective epidemiological investigation started in the provinces of Trento and Bolzano, where cases notified to the local health units were contacted.
It has been shown that among berries and vegetables those with uneven shapes are more likely to retain viruses on their surface, said the researchers.
A matched case–control study identified risk factors for HAV infection, from 1 January to 31 May 2013, in some regions where the largest increase in the number of cases was observed.
A case was defined as a symptomatic person, positive for HAV IgM with onset of symptoms (or date of testing if onset date not available) between those dates.
Potential controls that had not presented with hepatitis A symptoms during 1 January to 31 May 2013, were selected from the general population in the five Italian regions and matched with each case by age and place of residence.
The minimum sample size needed was estimated to be of 595 people (476 controls and 119 cases) and the data was collected via telephone interviews using an ad hoc questionnaire.
Sera and/or faecal samples were analysed by the Institute Experimental Zooprophylactic of Lombardy and Emilia Romagna (IZSLER) and the national reference laboratory at ISS for further characterisation by genotyping and sequencing
Retail frozen berry samples were analysed from food business operators. A reverse transcription-polymerase chain reaction (RT-PCR) was used to detect HAV.
To characterise the genotype of detected HAV strains, a nested PCR was performed with degenerate primers targeting the VP1-2a genomic region. Following purification, the VP1-2A region amplicons were subjected to double strand sequencing.
Source: Eurosurveillance, Volume 19, Issue 37, 18 September 2014
Authors: C Montaño-Remacha, L Ricotta, V Alfonsi, A Bella, M E Tosti, A R Ciccaglione, R Bruni, S Taffon, M Equestre, M N Losio, V Carraro, S Franchini, B Natter, M Augschiller, A Foppa, C Gualanduzzi, E Massimiliani, A C Finarelli, B M Borrini, T Gallo, V Cozza, M Chironna, R Prato, C Rizzo.