Case clustering in Hodgkin's disease: a brief review of the present position and report of current work in Oxford.

On this assumption many questions remain to be answered but some tentative conclusions can be drawn. 1. It would seem very likely that there is a transmissible HDA. 2. In this series, the time interval between the diagnosis of the infective patient and the diagnosis of the patient he in fected varied from 0 to 16 years, with a median of 3 years. The interval from the period of contact between the infec tive patient and the susceptible case and the time of diagno sis of the susceptible case varied from 0 to about 17 years with a median of about 6 years (this is all based on the assumption that patients did not meet each other after leav ing school). The latent period of HD has therefore a median of about 3 to 6 years; but it can be as brief as 1 to 2 years, and in most instances it is less than 10 years. 3. If the HDA is common then only a few people can in fect adults, and these are mainly HD patients and their immediate contacts. Expression of the 1st infection in adults as HD must be low unless either most people are infected in childhood when it must be assumed that expression of the infection as HD is negligible (cf. Epstein-Barr virus and infectious mononucleosis), or infection of adults is un common. 4. If the HDA is rare and HD patients are no more effec tive transmitters of the agent than others who have been infected, then expression of the infection as HD must be high. Without making assumptions about the relative effec-