The epidemiology of HBV in Italy has changed considerably over the last 20 years. Improved socio-economic conditions and hygiene and the introduction of the anti-HBV vaccination campaign led Italy to become a low HBV endemic country, with a prevalence of HBsAg carriers in the population of less than 2%20
On the other hand, increasing immigration from highly endemic countries has led to changes in HBV epidemiology. In addition to the higher prevalence of HBsAg among these subjects, even those who are negative display the highest prevalence of the markers of past infection31,32
. The global prevalence of anti-HBc in our study was 19.1%. This figure was partly due to the presence of non-Italians, among whom the prevalence was almost twice that among Italian subjects, thus reflecting their origin from countries in which HBV is still endemic.
There was no between-group difference in the prevalence of anti-HBs but, in the case of the simultaneous presence of anti-HBs and anti-HBc, the anti-HBs was more related to past infections among the non-Italians and to vaccinations among the Italians. This is best appreciated by observing the pattern of markers according to age. Among the Italians, the frequency of markers of past infection was low up to 30 years, but it was higher in the older age groups. This is due to a cohort effect, as the majority of the infections were acquired in the past. In contrast, the prevalence of anti-HBs alone (as a marker of a response to vaccination) was higher in the younger age groups mainly targeted by the vaccination campaign. In comparison with Italians, a smaller percentage of non-Italians had anti-HBs due to vaccination in all the age groups, whereas the prevalence of markers of past infection was always higher.
As far as the isolated anti-HBc pattern is concerned (anti-HBs negative/anti-HBc positive), its prevalence in the Italian subjects increases with age, and is as high as about 14% in those aged more than 50 years (probably due to a loss of anti-HBs in subjects infected long before). It is stated in the literature that an isolated anti-HBc pattern should be carefully evaluated because of false positive results of anti-HBc reactivity tests (particularly with enzyme immunoassays)33,34
. We used a screening enzyme immunoassay with a declared specificity of 99.75% and, in case of an isolated anti-HBc pattern, the positive results were confirmed by an enzyme linked fluorescent assay with a declared specificity of 99.94%, so our results can be considered sufficiently reliable.
It is possible that some of our cases with isolated anti-HBc may have had occult infection as there are published data on blood donors indicating an association between an isolated anti-HBc pattern and the concomitant presence of HBV DNA and infectious blood units35,36
. Moreover, HBV DNA has been found in the presence of anti-HBs as well as anti-HBc in the case of occult infections in blood donors37,38
. However, we could not investigate this any further because of the retrospective nature of our study. Another limitation of our work is the very small number of subjects younger than 11 years (only 31 subjects, data not shown) and the lack of data about the percentage of individuals with anti-HBs and anti-HBc or isolated anti-HBc who had been vaccinated.
In candidate blood donors the prevalence of markers of past infection and of vaccination are respectively lower and higher than in in-patients and out-patients, especially in the 31 to 50-year old age class, in which the major part of candidate blood donors can be found. However this group represents an healthy population, while (in- and out-)patients constitute a more varied population.
The comparison of data concerning Italian candidate blood donors with those obtained in a previous study on similar subjects in 1991 and 1999 clearly shows the decrease in the markers of past infection over time in all age groups, and a corresponding increase in the number of anti-HBs-positive subjects due to vaccination. The prevalence of HBsAg among the subjects who represent the generally healthy population in our area was 0.6% (currently in the course of publication). Non-Italians blood donors accounted for 1.8% of the total and, once again, they had a higher prevalence of markers of past infection than the Italians. The number of non-Italian blood donors is still very low in our area. Blood donation in Italy is not paid and does not, therefore, attract people seeking a means of increasing their income as in some other countries, but requires a certain level of cultural and economic integration. Probably only in the coming years will there be an increase of blood donors from recent waves of immigration. Unfortunately we have no data for anti-HBs and anti-HBc prevalence in the regular donors of 2007/2008, unlike those in 1991 and 199930
, since these tests were recently performed only on candidate blood donors.
In conclusion, as expected after the introduction of vaccination, the prevalence of the markers of past HBV infection in the Italian population of our area has decreased, but the increasing number of largely unvaccinated immigrants from highly endemic countries who show a high prevalence of the serological markers of active and past infections is redefining the epidemiology of HBV infection. This could be particularly important in transfusion medicine. The guidelines of the Italian Society of Transfusion and Immunohaematology (SIMTI) do not currently recommend an anti-HBc test to determine the eligibility of donors or blood components because its addition to testing for HBsAg and HBV-DNA seems to give no advantage to transfusion safety in the current epidemiological situation22
. The arrival of larger numbers of people from countries in which HBV is highly endemic, in association with a residual risk of transfusional HBV transmission which is still higher than that for other viruses (hepatitis C virus and human immunodeficiency virus), may lead in the near future to a revision of the prevention strategies for reducing transfusion risk.