Abstract A study on recrudescent typhus was conducted among 294 volunteers most of whom had contracted typhus in Eastern Europe and who immigrated to Israel after the Second World War. The main aim of the study was to determine whether persons, once infected, might subsequently suffer relapses without clinical signs which could presumably serve as sources of the microorganism in the interepidemic period and might be responsible for the initiation of new epidemics. The selection of volunteers was based on the reliability of their histories and on the absence of murine typhus in their present environment. Those under study were interviewed at regular 2-3 months' intervals during which blood samples were taken from them. Six blood samples were obtained from 262 individuals and at least 3 samples from the rest. Complement-fixation and microagglutination tests were carried out in order to establish the presence of antibodies specific for epidemic typhus. In 12% of the volunteers no demonstrable antibodies were found, while 67% considered to have such antibodies showed no significant titer fluctuations. However, 21% of the volunteers exhibited 4- to 8-fold fluctuations in titer in at least one of the tests used-a result which suggests the possibility of serological relapse.
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