Rosenau stated that under normal conditions 1 or 2 per cent of any population harbor virulent diphtheria. When an acute case of diphtheria occurs in a locality, the incidence is considerably increased (to about 14 per cent in institutions), and according to Schick2 it varies from 3 to 83 per cent. Zingher.3 found that the carrier rate in a community is even higher than that suggested by Rosenau, varying between 4 and 5 per cent.
Institutions, orphanages, camps, prisons, schools and state hospitals, or places which house an aggregation of many under one roof, serve as fertile soil for the spread of diphtheria. Therefore constant vigilance must be maintained to protect school children, inmates, patients and employees against this disease. Diphtheria carriers in a well protected community may be considered harmless. However they still are a menace to that portion of the population which lacks immunity, for in spite