The changing epidemiology of acute type B hepatitis: results of an 11-year prospective study in Padua (northern Italy).

The epidemiological pattern of acute type B hepatitis has been investigated in 1,107 consecutive patients during an 11-year prospective study conducted in Padua (Northern Italy) between 1978 and 1988. Remarkable changes were observed: 1) the attack rate of the disease increased significantly (p less than 0.05) between 1978 (18/10(5) inhabitants) and 1982 (29/10(5) inhabitants), particularly in male subjects and in the 15-19-year age group. The proportion of drug addicts also increased from 8.8 to 42% (p less than 0.05). These changes coincide in time with the spread of parenteral drug abuse in our area; 2) the attack rate dropped significantly (p less than 0.05) between 1983 and 1988 reaching the lowest levels ever observed before (4.7/10(5) inhabitants). The proportion of drug addicts decreased significantly (p less than 0.05), although the number of subjects starting narcotic abuse did not decline in recent years. Two major events could explain this pattern: a partial exhaustion of the susceptible population after spread of infection among drug abusers and, later on, the changing risk behaviours observed in our drug abusers after the AIDS prevention campaign. Other factors, including vaccination of some high risk groups, could have contributed to these changes.