Introduction and methods. Hepatitis A remains an important
public health problem in low endemicity areas, because of the
social and economic high burden of cyclical outbreaks. In this
study we described an outbreak of HAV infection occurred in the
city of Genoa and in its proximity and the viral circulation in the
post-epidemic period. In order to identify risk factors associated to
the illness and to determine the source of infection and the dynamics
of virus evolution, we conducted an epidemiological and molecular
investigation by a case-control study and by sequence analysis of
high variable regions of the genome.
Results. From May to October 2005, 58 HAV hepatitis cases were
notified. The case-control study showed that beach establishment
attending is strongly associated with HAV hepatitis (OR = 24.5,
p-value inf. 0.01), at multivariate analysis. The profile of epidemic
curve, the clinical onset of primary cases who occurred in few
weeks and the geographic distribution of cases clearly indicated
a common exposure to a point source: the outbreak can be probably
associated with a contaminated food product dispensed in
the affected area.
The outbreak has been mainly caused by a single variant, confirming
the common exposure to a point source; this variant previously circulated
within homosexual man (MSM) network in Northern Europe.
During the outbreak and in the following months, different variants
originating from Southeast Asia, Southern America and Northern
Africa, have co-circulated: all these cases were related to international
travel and none of these had determined secondary cases.
Discussion. The epidemiological picture of hepatitis A in Liguria is
characterized by a wide heterogeneity of circulating HAV strains.
This pattern could be associated with the increase of imported
cases and transmission within network of persons with similar risk
factors. Molecular approach coupled to descriptive and analytical
epidemiological studies appeared un-replaceable tools for management
and control of HAV outbreaks, because of their capacity
to recognize infection origin, transmission patterns and dynamics
of virus evolution.