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There are 6 epidemic models of hepatitis A in the world.In China

there are 3 mod-els

namely

Beijing

Shanghai and Guangzhou models.In 1979

Schenzle proposed a modifiedsimple catalytic model whose force of infectivity is a logistic function.We made a modifiedmodel with the infectivity force of a linear or conic function.According to the actual data

theauthors have fitted 3 epidemic models.The results are satifactory as proved by the x

2

-test ofgoodness of fit.The analysis of the models indicates that the force of infectivity has been lower inShanghai than in Beijing and Guangzhou since·1970.An interesting finding is that the differencebetween the 3 epidemic models is due to the function of infectivity force of hepatitis A.