A total of 8124 individuals, of whom 5801 were males and 2323 were females, have been studied to determine the extent of Brucella infection and immunity.
The status of the individuals regarding Brucella infection and immunity was determined by the aid of the Brucellergin skin test, the opsonic test, the agglutination test, blood, stool and urine culture.
Of the total number examined, 845 or 10.3 per cent gave a positive skin test; 7.1 per cent were classified as infected; 2.7 per cent as immune, and 0.52 per cent as questionably immune.
No significant differences were noted between the incidence of infection and immunity in male and female groups.
The size of the skin reactions in approximately 50 per cent of those individuals who were positive fell between 25 and 75 mm.
Of the 222 classified as immune, 47.3 per cent showed insignificant serum agglutination titers. Of the 436 classified as infected, 90.5 showed insignificant agglutination titers.
In a re-test of 99 negative individuals after an interval of five months, 9 were found to have developed an allergy to Brucella during the interval. Of those, 5 were classified as infected and 4 as immune. In a re-test of 103 individuals previously classified as infected, 3 had become negative, 33 immune and 69 were still classified as infected. Of the 84 re-tested in the immune group, 80 retained the same classification and 4 were classified as infected.
The allergic response to four different dilutions of Brucellergin was compared in 185 Brucella sensitive individuals. When a dilution of Brucellergin higher than 1:2,000 is employed, a slight decrease is noted in its activity.
The 1:2,000 dilution should always be used for diagnostic purposes, but for epidemiological surveys in the general population, a dilution of 1:25,000 may be employed with a high degree of accuracy.