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The identification of two types of infectious hepatitis with distinctive clinical, epidemiological, and immunological features provided an explanation for the occurrence of second attacks of the disease. One type resembled classical infectious hepatitis (IH); it was characterized by an incubation period of 30 to 38 days, a relatively short period of abnormal serum transaminase activity (3 to 19 days), a consistently abnormal thymol turbidity, and a high degree of contagion. The other type resembled serum hepatitis (SH); it was characterized by a longer incubation period (41 to 108 days), a longer period of abnormal transaminase activity (35 to 200 days) and a relatively normal thymol turbidity. Contrary to commonly accepted concepts, the SH type was moderately contagious. Patients with IH type were later proved to be immune to the same type. Patients with the SH type were not immune to the IH type infection.
Saul Krugman (Mon,) studied this question.