From these studies it is apparent that the question of histoplasmin sensitivity and its relationship to pulmonary calcification is one which may be of great importance in one locality and of no importance in another; and also that some factors of climate and physical geography must be of great significance in the epidemiology of histoplasmin sensitivity.
Our studies show that there is a wide variation in the prevalence of sensitivity from one area to another within the State of Tennessee and in neighboring states (7). Indeed, the extensive studies reported by Palmer (27) and by Prior and Allen (29) showed that there was in other states a similar variability.
Furthermore, the wide variation in sensitivity observed in our studies in students from different states shows that the variation is in relation to a fairly definite geographic focus and is suggestive of an infectious agent existing commonly in an area where climatic factors favor its propagation. Indeed, throughout these studies wherever histoplasmin sensitivity is high, pulmonary calcification is also high. A similar relationship has been recognized in the problem of coccidioidomycosis, an infection in which sharply delimited foci of propagation and infection have been demonstrated.
The examination of the geographic pattern of histoplasmin sensitivity is of interest because it gives some indication of the relative presence or absence of the infection in a given area.
Our own experience and that of others in different parts of the world with histoplasmin for a skin testing material is herein summarized. The use of the test as an epidemiologic index of infection with H. capsulatum is suggested. It is evident that these studies point out the need for skin testing with tuberculin as well as other fungous antigens in areas where pulmonary calcification is prevalent in nonreactors to tuberculin or where healed or healing pulmonary esions do not reveal tubercle bacilli or other causative organisms.
From the Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee.