Of 1586 patients in institutions in North Carolina, 17.7 per cent gave positive skin reactions to trichinella antigen. The incidence of infections as determined by this method is in contrast to that found at autopsy in this area (2.8 per cent). This discrepancy has been attributed to the presence of light subclinical infections difficult to detect at autopsy; but it is possible that other factors, such as intercurrent disease, may have altered the incidence of positive skin tests in this study.
18.3 per cent of 674 tuberculous patients in sanatoriums and 17.2 per cent of 912 non-tuberculous patients in institutions (chiefly mental patients in psychiatric hospitals) gave positive reactions. In a previous study 6.9 per cent of 422 patients in general hospitals were found to give positive reactions.
The possibility is discussed that the type and stage of intercurrent disease may be a more important factor in reactivity to trichinella extract than is confinement in an institution, and that reactions to trichinella skin tests may be unreliable during a period of mental illness.
The incidence of positive skin tests was found to be greatest in patients confined in an institution for eighteen to twenty-nine months.
Race, sex, and residence in urban or rural areas are not significant factors. The incidence of pesitive skin tests decreases with advancing age.
The occurrence of delayed and persistent positive tests cannot be explained on the basis of very recent infection alone.