Between January and May 2013 a hepatitis A (HA) incidence increase was detected in Italy, signalling an
outbreak. A retrospective matched case–control study
was conducted to identify the source of infection. A
case was defined as a resident of any of five regions
(Apulia, autonomous province of Bolzano, EmiliaRomagna, Friuli–Venezia-Giulia and autonomous
province of Trento), who had symptom onset between
1 January and 31 May2013 as well a positive test for
anti-HA virus IgM. We compared each case with four
age-and neighbourhood-matched controls. Overall 119
cases and 419 controls were enrolled. Berries were
found as the main risk factor for HA (adjusted odds
ratio (ORadj): 4.2; 95% confidence interval (CI): 2.5–
7.0) followed by raw seafood (ORadj: 3.8; 95% CI: 2.2–
6.8; PAF: 26%). Sequencing the virion protein (VP)1-2a
region from 24 cases yielded a common sequence
(GenBank number: KF182323). The same sequence
was amplified from frozen mixed berries consumed
by some cases as well as from isolates from Dutch
and German HA patients, who had visited some of the
affected Italian provinces during the outbreak. These
findings suggested berries as the main source of the
Italian outbreak. Control measures included voluntary
recall of the confirmed frozen mixed berry batches and
a trace-back investigation was initiated. The Ministry
of Health website recommends frozen berries to be
cooked for two minutes before eating.