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Histoplasmin, Tuberculin and Coccidioidin Sensitivity on the Isthmus of Panama: Preliminary Report of 500 Patients¹

Five hundred patients were tested intradermally with histoplasmin, tuberculin and coccidioidin on the wards of Colon Hospital, Panama Canal Zone. Histoplasmin (1:100) produced induration five or more millimeters in diameter in 190 (38.0 per cent). Two separate sources of antigen were used; results were entirely comparable. A total of 302 patients (60.4 per cent) reacted to test injections of 0.0005 milligram of P. P. D., of whom 142 were also histoplasmin-positive. Coccidioidin (1:100) produced reactions in only two patients; two separate sources of material were employed, these patients giving responses to both. These tests provided adequate control.

There was no evidence that sex, race or geographic background influenced the incidence of histoplasmin sensitivity. Age was a significant factor; culmulative curves started at zero (newborn infants) and rose sharply during the second, third and fourth decades with gradual leveling off thereafter.

There is an obvious discrepancy between the finding that 38.0 per cent of the patients tested reacted to histoplasmin and the fact that there has been no recognized case of human histoplasmosis proven on the Isthmus of Panama since 1906. Further studies are in progress to determine whether the high incidence of histoplasmin sensitivity is due to cross reactions in patients who have had infections with antigenically related fungi, to direct exposure to H. capsulatum, or to the operation of both factors.

¹ From the Medical Service, Colon Hospital, Cristoba, Panama Canal Zone.