European Journal of Epidemiology 10: 633-635, 1994. © 1994 Kluwer Academic Publishers. Printed in the Netherlands BRIEF REPORT Decline in anti-HAV prevalence in the Milan area between 1958 and 1992 A.R. Zanetti 1, L. Roman61, E. Tanzi 1, A. Andreassi 1, A. Pozzi 1, A. Panuccio ~ & T. Stroffolini 2 1Institute of Virology, University of Milan; 2 National Institute of Health, Rome, Italy Accepted in revised form 22 April 1994 Abstract. We have compared the prevalence of antibody to HAV in sera collected from healthy individuals of Milan in 1958, 1977 and 1992 respec- tively. The results show a dramatic reduction of HAV Key words: Anti-HAV, Hepatitis A, Seroepidemiology circulation likely due to the considerable improve- ment of socioeconomic and hygienic living condi- tions which have occurred in Italy during the last decades. Hepatitis type A is a wide-spread infectious disease, especially common in developing countries. Italy has been considered for a long time at intermediate endemicity for hepatitis A virus (HAV), where infection was mainly acquired subclinically in early childhood. More recently in Italy as seen in other industrialized countries, the incidence of acute hepatitis A has been shown to decline over time. This pattern is consistent with the steady decrease in anti- HAV prevalence which has been observed among Italian children and adolescents during the last few decades [1-5]. In Milan, a previous study comparing the anti-HAV prevalence in different age groups between 1958 and 1977 showed a remarkable drop in the presence of antibody, especially among the youngest individuals (35.7% versus 3.6% in subjects 1-5 years old and 78.6% versus 26.9% in those 6-15 years old, respectively) [5]. In order to assess the current level of HAV circu- lation in the same area, we have examined by enzyme immunoassay (HAVAB-EIA, Abbott Labs, USA) 1109 serum samples collected in t992 from healthy individuals of Milan. This seemed to us a good opportunity to study the seroepidemiological trend of anti-HAV infection over a very long period of time (1958-1992). As shown in Figure 1, the current age-dependent prevalence curve shows a typical sigmoidal shape, characterized by a low percentage of anti-HAV presence during childhood, a sharp increase in adulthood and a high level of antibody positivity among persons over 50 years of age. Between 1958 and 1992, the overall anti-HAV prevalence declined from 91.1% (215/236) in 1958, to 76.8% (335/436) in 1977 to 25.0% (277/1109) in 1992. No difference was found among genders in the three periods examined. The percentage of anti-HAV reduction resulted significantly higher (p < 0.01, by X 2 test) during the period 1977-1992 than in the period 1958-1977. As shown in Figure 2, the decline of anti-HAV affected mainly the younger age groups. In 1958, the anti- HAV age-specific prevalence in individuals 1-5 years old, 6-15 years old and in those 16-30 years old was 35.7%, 78.6% and 93.3%, respectively, while the corresponding figures in 1992 were 2.2%, 3.3% and 8.1%, respectively. On the contrary, similar anti-HAV prevalences were found among individuals aged over 50 years, independent of the year of sampling (Figure 2). Thus, during the last decades, as a consequence of a reduction of HAV circulation in our area, we have observed a considerable drop in anti-HAV positivity, especially among subjects under 30 years of age. The very high proportion of immune persons found in the older age groups should be interpreted as a cohort % anti-HAV positive 1 O0/I 80 60 4O 20 0 1-5 6-15 Age groups (years) 16-30 31-40 41-50 ,50 148/158 Figure 1. Age-specific prevalence of anti-HAV in the Milan, Italy, area in 1992.